Breakneck and Double-quick

Breakneck adjective - Moving, proceeding, or acting with great speed.

Double-quick and breakneck are semantically related In some cases you can use "Double-quick" instead the word "Breakneck" as an adverb or an adjective.

Double-quick adjective - (of a marching cadence) very quick.

Breakneck and double-quick are semantically related in fast topic. Sometimes you can use "Breakneck" instead the phrase "Double-quick" as an adjective or an adverb, if it concerns topics such as very fast.