n. An unusual and un-English assimilation of in- before l, after the analogy of or by confusion with il-, il-: perhaps only in the rare and obsolete illighten for inlighten, enlighten (compare alighten).n. An assimilation (in Latin, etc.) of in- before l. (See in-.) In the following words, in the etymology, the prefix il- is usually referred directly to the original in-.n. An assimilation (in Latin, etc.) of the negative or privative prefix in- before l. (See in-.) In the following words, in the etymology, the prefix il- is usually referred directly to the original in-.n. A suffix of Latin origin, forming in Latin adjectives and nouns derived from them, and less frequently nouns directly from verbs and nouns, many of which formations have come into English.A simplified spelling of ill.