Occasionally the Latin language attached the suffix –ārius to a noun in order to form a 1st and 2nd declension adjective with the usual general meaning, “pertaining to”:
rota (“wheel”) > rotarius > E rotary
honor (“honour”) > honorarius > E. honorary (and honorarium)
ordo, ordin-is (“rank,” “order”) > ordinarius > E ordinary
imago, imagin-is (“likeness”) > imaginarius > E imaginary
Notice, by the way, that we have already met the adjective ordinalis, yet here we find ordinarius. It is uncommon in Latin to have two alternative forms like these, and they will usually have arisen at different periods in history. Also, you should realize that it is hard to predict a Latin source for an English word in -ary, since this suffix may derive from either –aris (military) or –arius (ordinary). Of the two possibilities, –arius is by far the more likely original suffix for any word ending in –ary.
Latin adjectives in –arius were sometimes used as masculine or neuter nouns, creating two groups of words that have a good many English derivatives:
- The masculine form –arius often meant “a person working or engaged in —–”. A person working in stones (lapis, lapid-is) is a lapidary (< lapidarius); a person entrusted with a secret (secretum) is a secretary (< secretarius); and a man who carries water (aqua) is Aquarius, a sign of the zodiac. In Middle English, this ending might be transformed into -er: L plumbarius , “a worker in lead” (plumbum) > plumber.
- The neuter form –arium came to suggest “a place for ——”. Several of these words still survive in English in their original Latin spelling—aquarium (“a place for water”), solarium (“a place for sun”). Others have evolved regularly into words that end in –ary. An aviary is a place for birds, a granary a place for grain, an ovary a place for eggs, and a mortuary a place for the dead.
- Even the Romans apparently found these suffixes confusing: auxilium (“help”) had two adjective derivatives, auxiliaris and auxiliarius, and E auxiliary (= “helpful”) is thought to have derived from the second. The similar English word ancillary is derived from ancillaris, “like a maidservant” (ancilla). ↵