Fly by night and Spur-of-the-moment

Spur-of-the-moment and fly by night are semantically related. in made-up topic. In some cases you can use "Spur-of-the-moment" instead an adjective phrase "Fly by night".

Spur-of-the-moment adjective - Made or done without previous thought or preparation.

Fly by night and spur-of-the-moment are semantically related. Sometimes you can replace phrase "Fly by night" with "Spur-of-the-moment", this phrases are similar.