Nightly means happening every night, or relating to the nighttime. A family might have a nightly routine of reading together before bed. A security guard might make nightly rounds through a building, checking every door and window after dark.

The word appears frequently in phrases like nightly news (a TV broadcast that airs every evening) or nightly performances (when a theater company puts on the same show each night of the week). If you take a vitamin nightly, you take it once per night, every night.

Notice that nightly is different from nocturnal, which describes creatures that are naturally active at night, like owls or bats. Nightly simply describes something that happens regularly when night falls, whether it's a meteor shower you can observe nightly in August, a bakery that does its nightly cleanup, or the nightly cooldown in temperature as the sun sets. The word captures that steady, predictable rhythm of things that happen when darkness arrives.