From Middle English -ly, -li, -lik, -lich, from Old English -līc, -līċ, from Proto-Germanic *-līkaz (“having the body or form of”), from *līką (“body”) (whence lich). In form, probably influenced by Old Norse -ligr (“-ly”). Cognate with Dutch -lijk, German -lich and Swedish -lig, and with English -like (from Proto-Germanic *līka-).
- Used to form adjectives from nouns, the adjectives having the sense of "like or characteristic of what is denoted by the noun".
- Used to form adjectives from nouns specifying time intervals, the adjectives having the sense of "occurring at such intervals".
In prescriptive usage, derived adverbs in -ly are often preferred to those which are identical in form to the base adjective (e.g., badly instead of bad), despite the fact that the latter have been in continuous use since the earliest stages of the language and represent the norm in languages closely related to English, such as Dutch and German. This is the cause of hypercorrections such as I feel badly (where feel actually represents a copular verb, which traditionally requires an adjectival complement rather than an adverb).
Various sound changes and spelling changes occur for -ly:
- If an adjective ends with a consonant followed by y, it changes into i before adding the suffix (e.g. ready > readily, easy > easily).
- If an adjective ends with ll, one l drops out to avoid a triple letter (e.g. full > fully, shrill > shrilly).
- If an adjective ends with a syllabic /l̩/ (spelled -le after a consonant), euphony causes the -le to drop out. Examples include -ably and -ibly, but also noble > nobly, ample > amply, and idle > idly, among others.
- Adjectives ending in -ic generally take -ally (public > publicly being an exception).