The term "crack off" refers to the act of breaking or separating something from a larger piece. The opposite of this term is "attach," which means to connect or fasten something to another item. Other antonyms for "crack off" include "merge," which means to blend two things together, "join," which means to link or combine two or more items, and "fuse," which means to melt two objects together. These antonyms are often used in situations where you want to combine or connect objects, rather than breaking them apart. Understanding antonyms can enrich your vocabulary and improve your communication skills.