The term "fly-by-night" is used to describe things or people who are unreliable or untrustworthy. Antonyms of this word are those that represent the opposite meaning. Some of the antonyms for "fly-by-night" are stable, dependable, trustworthy, and reliable. These words imply that someone or something is consistent, accountable, and capable of being relied on. A stable business or organization has been around for a long time and has a proven track record. A dependable employee shows up on time, performs consistently, and is reliable. Trustworthy people can be trusted with sensitive information and are honest and upfront about their intentions. In summary, antonyms for "fly-by-night" connote dependable, reliable, and trustworthy traits.