The adverb has 2 meanings:
Meaning #1:
to a moderately sufficient extent or degree
Synonyms: moderately, within reason, somewhat, fairly, middling, passably
Antonym: unreasonably (meaning #2)
Derived from adjective: reasonable (meaning #2)
Meaning #2:
with good sense or in a reasonable or intelligent manner
Synonyms: sanely, sensibly
Antonym: unreasonably (meaning #1)
Derived from adjective: reasonable (meaning #3)
