Not necessarily. Not all adverbs end in ”-ly”, e.g. ”fast” as in ”He talks fast.” However the vast majority of them does. The ”ly” ending is the descendant of an Old English form ”-lich”, which has undergone some transformations from the Middle Ages up to now. On the contrary, there other kinds of word that happen to end in ”-ly”. For such words we cannot really talk about an ending as with the adverbs. A couple of nouns end accidentally in ”-ly”, such as ”family”, ”fly” or ”ply”. There are adjectives as well: ”sly, ”girly” [this one has a ”-y” ending, though!], ”courtly”...have a look at this wiki page, it may be useful: https://polyglotclub.com/wiki/Language/English/Grammar/Adjectives-ending-in-ly
vincentFebruary 2021thanks for your answer ! thanks for the reference to the wiki page.
|XopheFebruary 2021|vincentFebruary 2021thanks!
Many (dare I say most?) of them are, but by no means all. As a general rule, words deriving from [adjective] + -ly are adverbs, while words deriving from [noun] + -ly are adjectives.
To name a few non-adverbs ending in ”-ly”:
Comely, family, jelly, hilly, silly, clinodactyly, wily, daily, friendly.