NIGHTLY is an adjective that describes something that happens or occurs every NIGHT. It is related to the words NIGHT, NIGHTTIME, and NOCTURNAL. NIGHT is a 5-letter word that refers to the period of darkness between sunset and sunrise. NIGHTTIME is a 9-letter word that is synonymous with NIGHT and is used to describe the hours of darkness. NOCTURNAL is also a 9-letter word that means active during the NIGHT. All three words are related to the term NIGHTLY and describe activities or events that take place during the NIGHT.