Fleetly and Flat-out

Fleetly adverb - With great speed.

Flat-out and fleetly are semantically related. in fast topic. In some cases you can use "Flat-out" instead an adverb "Fleetly", when it comes to topics like immediately, speedily, very fast, very quickly.

Flat-out adjective - Having no exceptions or restrictions.

Fleetly and flat-out are semantically related. Sometimes you can use "Fleetly" instead an adverb phrase "Flat-out".