phosphoro-comb. form
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Stress is usually determined by a subsequent element and vowels may be reduced accordingly; see e.g.
phosphoroscope n.Origin: Formed within English, by compounding. Etymons: phosphorus n., phosphor n., -o- connective.
Etymology: < either phosphorus n. or phosphor n. + -o- connective.Apparently earliest in phosphorochalcite n., after German. Found in a small number of formations within English (earliest in the mid 19th cent. in phosphorogenic adj., perhaps after French; compare also phosphoroscope n., phosphorograph n.). Some formations with a second element beginning with a vowel, such as phosphoryl n., could alternatively be interpreted as derivatives of phosphorus n. (as are all earlier such words, e.g. phosphorous adj., phosphoric adj., phosphorescent adj., etc.).
This entry has been updated (OED Third Edition, March 2006; most recently modified version published online January 2018).