Nightly means happening every night. A nightly ritual, nightly performances, nightly news.
It is the night counterpart of daily and works as both adjective and adverb — a nightly walk, he walks nightly — which is a small oddity English allows in this family. Nightly news is the American term for the evening bulletin. Note the trap with nocturnal, which means active at night rather than repeated every night: an owl is nocturnal and a bulletin is nightly, and they are not interchangeable.
1adjectivenightlyHappening every night.
“The nightly news comes on at ten o'clock.”
2adverbadverbEvery night.
“The show is performed nightly throughout the summer.”
nightly is a frequency.
Old English nihtlic is night plus -lic, the ancestor of -ly. Daily, weekly and yearly are built the same way, and the pattern is older than the Norman conquest.
Old English
nihtlīċ
Middle English
nyȝtly
English, today
nightly
Built from
From Middle English nyȝtly, nihtlich, nihtlic, from Old English nihtlīċ, nihtelīċ (“nocturnal, nightly, of the night, at night”), equivalent to night + ly. Cognate with Scots nichtlie (“nightly”), West Frisian nachtlik (“nightly, nocturnal”), Dutch nachtelijk (“nightly, nocturnal”), German nächtlich (“nocturnal, nightly”), Danish natlig (“nightly”), Swedish nattlig (“nightly, nocturnal”).
Etymology from Wiktionary, CC BY-SA