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 replace phrase "Double quick" with "Breakneck", this terms are similar.

Double quick adverb - At a faster speed.

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.