ETYM Latin adverbium; ad + verbum word, verb: cf. French adverbe.
1. A word that modifies something other than a noun.
2. The word class that qualifies verbs or clauses.
Grammatical part of speech for words that modify or describe verbs (“she ran quickly”), adjectives (“a beautifully clear day”), and adverbs (“they did it really well”). Most adverbs are formed from adjectives or past participles by adding -ly (quick: quickly) or -ally (automatic: automatically).
Sometimes adverbs are formed by adding -wise (likewise and clockwise, as in “moving clockwise”; in “a clockwise direction”, clockwise is an adjective). Some adverbs have a distinct form from their partnering adjective; for example, good/well (“it was good work; they did it well”). Others do not derive from adjectives (very, in “very nice”; tomorrow, in “I’ll do it tomorrow”), and some are unadapted adjectives (pretty, as in “It’s pretty good”). Sentence adverbs modify whole sentences or phrases: “Generally, it rains a lot here”; “Usually, the town is busy at this time of year.” Sometimes there is controversy in such matters. Hopefully is universally accepted in sentences like “He looked at them hopefully” (“He looked at them full of hope”), but some people dislike it in “Hopefully, we’ll see you again next year” (“We hope that we’ll see you again next year”).