An unusual and un-English assimilation of in- before l, following the example of or by confusion with il-, il-: possibly only in unusual and outdated illighten for inlighten, illuminate (compare alighten).
An assimilation (in Latin, etc.) of in- before l. (identify in-.) Into the following words, inside etymology, the prefix il- is generally known straight to the original in-.
An assimilation (in Latin, etc.) of this unfavorable or privative prefix in- before l. (See in-.) In following terms, in etymology, the prefix il- is usually referred right to the original in-.
A suffix of Latin origin, developing in Latin adjectives and nouns derived from them, much less regularly nouns right from verbs and nouns, some of which structures have come into English.