Which word is NOT a synonym for "cancel"?

The correct choice is the word "approve," as it does not share a similar meaning with "cancel." When you cancel something, you are effectively nullifying or ending its existence or planned occurrence. In contrast, to approve means to agree to or accept something, which is the opposite of canceling.

On the other hand, "call off," "postpone," and "terminate" all relate to the concept of canceling in some way. "Call off" means to stop an event that was planned. "Postpone" implies delaying something to a later time, which can also be seen as a form of cancellation, although with the intention to reschedule. "Terminate" means to bring something to an end, which directly aligns with the meaning of canceling. Thus, "approve" stands out as the only word that does not relate to the idea of canceling.