Etymology: < Anglo-Norman ajuster, adjuster, (with change of conjugation) adjoustre, Anglo-Norman and Middle French adjouster, ajouster (Old French, Middle French, French ajouter) to add or join (a thing) to (another thing) (1119 in Old French) < a- a- prefix⁵ + joster , jouster , juster , etc. joust v. The French verb shows extensive formal overlap, and also semantic points of contact, with ajuster , †adjuster adjust v.² (see discussion at that entry), which is reflected in the English forms with medial -u- . Perhaps compare post-classical Latin adiuxtare in uncertain sense, perhaps ‘to place beside’ (in an undated saint's life; probably < French (compare the Middle French variant spelling adjouxter )). Sense 1 appears to lack a parallel in French.Quot. 1530 at sense 2 suggests that the word was obsolete by 1530. Compare later adjute v., which shows a reborrowing of the same French verb. In to adjust faith to after Anglo-Norman ajuster fei a, Middle French ajouster foi a (12th cent. in Old French as ajoster fai a ; French ajouter foi à ; > Italian †aggiustare fede a (14th cent.)) and Middle French ajouster credence a, ajouster creance a (late 14th cent.). The β. forms reflect the French forms in ad- and their ulterior model, classical Latin ad- ad- prefix.

Etymology: < French †adjuster (now ajuster) to harmonize (different things) (1260 in Old French as ajouster ; 1480 with specific reference to mechanical apparatuses), to reconcile (discordant things or people) (16th cent. in Middle French), to adapt oneself to (something) (16th cent., used reflexively), to arrange or neaten (one's own, or occasionally another's, clothing, appearance, etc.) (1659), to adorn, deck out (a person) (1680, originally used reflexively) < a- a- prefix⁵ + juste just adj. Compare Catalan ajustar (1696), Portuguese ajustar (14th cent.), Italian aggiustare (mid 13th cent.), which all directly or indirectly show prefixed verbs formed from the respective parallels of just adj.In β. forms perhaps after Middle French (rare) adjouster (first half of the 14th cent.; also c1450 as adjouter ), variant (influenced by adjouster adjust v.¹) of adjuster (although most instances of the French verb in a spelling with medial -ou- could actually be taken as showing adjouster adjust v.¹). Association of the β. forms with earlier adjust v.¹ within English is unlikely on semantic grounds. Especially in the Old French and Middle French periods, the French verb shows both formal overlap and semantic points of contact with the French verb now spelt ajouter (see adjust v.¹), which ultimately reflects classical Latin iuxtā near, beside (see juxta- prefix). This overlap and confusion is also evidenced by post-classical Latin adjustare (13th cent., originally and chiefly in French sources; < French), which also occurs in the variant spellings adjoustare , ajoustare (in an undated saints' life). Compare also Spanish ajustar , which is attested from the first half of the 13th cent. onwards in a large number of senses ranging from ‘to join, attach, unite’ to ‘to harmonize, reconcile’ and ‘to rectify’ (with the now predominant senses, all closely linked to justo just adj., only appearing in the 16th cent.), and shows a merger of two etymologically distinct verbs (one ultimately derived from classical Latin iuxtā, the other from classical Latin iūstus); see further Diccionario histórico de la lengua española (1972) at ajustar v.¹