As "de-truncate" technically means to restore something that was cut short to its original length, there are several antonyms for this word depending on the context. For instance, if one is using "de-truncate" in the field of mathematics or geometry, antonyms could include "truncate," "shorten," or "abbreviate." However, if one is speaking in metaphorical terms, possible antonyms could include "prolong," "extend," or "stretch out." In any case, using the proper antonym for "de-truncate" can help convey the intended meaning of a sentence more accurately and succinctly.