I. ˈnītlē, -li adjective
Etymology: Middle English nightly, nihtlich, from Old English nihtlīc, from niht, n., night + -līc -ly
1. : of or relating to the night or every night
peering into the nightly murk — Springfield (Massachusetts) Union
2. : happening, done, or used by night or every night
giving five-minute nightly analyses of the news — Current Biography
II. adverb
Etymology: Middle English, from nightly, adjective
: every night
gathered nightly to listen to the band concerts
also : at or by night