Etymology: < post-classical Latin -o-, a connecting vowel occurring in compounds formed by analogy with Greek compounds (and classical Latin compounds borrowed from them) in which the first element ended in -ο ; this was originally the nominal stem of the first element (as in δημοκρατία democracy n.) and was later added to other first elements by analogy (as in μητρόπολις metropolis n.).Classical Latin -o- appears mainly in words borrowed from Greek, e.g. classical Latin philosophia philosophy n., thermopolium thermopolion n. This continues to be true in post-classical Latin until the 16th cent.; there are also similar formations which originate in post-classical Latin but are from Greek elements, e.g. typographia (15th cent.: see typography n.), and chalcographia (16th cent. or earlier: see chalcography n.), or from one Latin and one Greek, e.g. Nizoliodidascalus (1573), the title of a response to the writings (in Latin) of Nizolius. However, Latin also has a few original compounds in -o- where the -o- should probably be regarded not as a simple nominal suffix, but as a Latin ablative or adverbial ending, e.g. classical Latin sacrōsanctus , post-classical Latin primōgenitus (see primogenit n.), and possibly post-classical Latin aurotextus (from 12th cent. in British sources). These original Latin compounds do not seem to have been the model for any native English compounds, with the possible exception of serio-comic adj. and n. (1783). Classical Latin also had a few compounds where the -o- is the nominative ending, rather than the stem or an extension of the stem, e.g. sermōcinārī (see sermocination n.), lēnōcinium lenociny n., and words formed analogically with these, e.g patrōcinium patrociny n. Most other original formations in post-classical Latin using -o- may be divided roughly into three groups. (i) Those formed on the analogy of compound ethnonyms in Greek, or of ethnonyms borrowed into Latin from Greek; very few of these are earlier than 16th cent. (ii) Terms describing branches or methods of study; very few of these are earlier than 17th cent. (iii) Technical terms in the physical sciences; very few of these are earlier than the second half of 17th cent. Exceptions to the relatively late appearance of compounds in -o- outside Greek include compounds of pseudo- pseudo- comb. form, which is productive from classical Latin on; compounds of philo- philo- comb. form, which is productive from early post-classical Latin on; and a few post-classical Latin words beginning with theo- theo- comb. form and deo- . Ethnonyms in -o- , and similar adjectives referring to geographical or linguistic origin, which are found already in classical Latin include Gallograecus (see Gallo-greeks n. at Gallo- comb. form1 1b), Syrophoenix (see Syrophœnician n.); and in early post-classical Latin Gallohispani (Jerome). Much more recent formations in post-classical Latin include Anglo-Saxonicus (17th cent.: compare post-classical Latin Anglo-Saxo (12th cent.; rare until 15th cent.) compared with the earlier form Angul-Saxo (from 10th cent.): see Anglo-Saxon n. and adj.) and Graecolatinus (1478 or earlier: compare Graeco-Latin at Graeco- comb. form 1). Most examples before c1500 appear to occur in Latin titles of lexica, where the first element is usually Latino- or Graeco- , e.g. Vocabularium Latinogermanicum (1467), and it is possible that the diffusion of this usage in the titles of printed books was a major factor in promoting new formations of compound ethnonyms in -o- . Three elements are linked in Latinograecogallicus (1573 in the title of a lexicon). Compounds following this pattern are found in post-classical Latin describing kinds of study, where the branches of learning described by each element overlap or are combined. Examples include iatro- iatro- comb. form (1573 in iatromathematicus ), medico- medico- comb. form (1597), mechanico- mechanico- comb. form (1630), historico- historico- comb. form (early 17th cent.), philosophico- philosophico- comb. form (early 17th cent.). Three-element compounds of this kind developed quickly in Latin, e.g. juridico-historico-politicus (1635), historico-politico-juridicus (1651), medico-chemico-chirurgicus (1658), politico-juridico-historicus (1668), historico-politico-juridicus (1673). Most of these compounds were formed first in post-classical Latin, but iatromathematicus reproduces Hellenistic Greek ἰατρομαθηματικός (see iatromathematical adj.). Examples of technical and scientific terms found already in classical Latin include haemorrhois haemorrhoid n.2, petroselīnum petroseline n., both loanwords from Greek. Examples of new formations in post-classical Latin from Latin elements include plano- plano- comb. form1 (1658 in plano-geometria ); from Greek elements, ophthalmo- ophthalmo- comb. form (1615 ophthalmoscopia , 1648 in ophthalmographia ). In English, the element is found earliest in borrowings of Latin and Greek combining forms, from the Middle English period onwards, such as those listed above in conjunction with the Latin forms cited. The earliest native formations with this element are on Greek and Latin bases which did not have a combining form or stem vowel in -o in the original languages. An example from the 16th cent. is meco- comb. form (in mecometry n.); from the 17th cent. come martyro- (in martyrologe n.), martyrio- (in martyriologer n.), naso- comb. form (in naso-spirital at naso- comb. form 1 and naso-vocal at naso- comb. form 1), concavo- comb. form (in concavo-convex n. at concavo- comb. form ), and plano- comb. form1 (in plano-solid adj. at plano- comb. form1 3); similar, or perhaps formed on the English equivalents, are Papisto-mastix n., Puritano-mastix n. In the 18th cent. appear definite formations on English words, such as negativo- comb. form (in negativo-affirmative ), Normanno- comb. form (in Normanno-Saxonic at Normanno- comb. form ), Dano- (in Dano-Saxonic ), and Methodistico- comb. form (in Methodistico-Monkish ). In the same century this element is found attached to English words in scientific and technical combining forms, e.g. magnetico- comb. form (in magnetico-electrical ), nervo- comb. form (in nervo-ligamentous adj. at nervo- comb. form ). From around 1800 onwards, formations on stems of all kinds become common, e.g. medio- comb. form, molybdo- comb. form1, moto- comb. form, murio- comb. form, and such isolated coinages as bancomania n. and Queenomania n. There are some suffixes and combining forms before which -o- regularly appears, and where it tends to be treated as if it were part of the termination, particularly where the latter is combined with an English first element which ends in a consonant. Examples include -ocracy comb. form (for an example with a vowel, compare the variant bureau-ocracy at bureaucracy n. Forms), -ography comb. form, -ology comb. form, -ometer comb. form. Compare classical Latin -olentus (after uiolentus) in e.g. uinolentus, somnolentus.
This entry has been updated (OED Third Edition, March 2004; most recently modified version published online March 2022).
/əʊ/, U.S. 
connective