what does the phrase fly by night mean
â¢ FLY-BY-NIGHT (noun). The noun FLY-BY-NIGHT has 1 sense: 1. a debtor who flees to avoid paying. Familiarity information: FLY-BY-NIGHT used as a noun is very rare. â¢ FLY-BY-NIGHT (adjective). The adjective FLY-BY-NIGHT has 2 senses: 1. of businesses and businessmen of questionable honesty. 2. ephemeral. Familiarity information: FLY-BY-NIGHT used as an adjective is rare.