Answer:
Crucial-necessary
Explanation:
The combination of words "crucial" and "necessary" are the only two that match in this question. The word "crucial" refers to something that is of highest, greatest, or most critical importance. On the other hand, the word "necessary" refers to something that is essential, needed or unavoidable. Therefore, we can conclude that the word "necessary" could also be a possible definition of the word "crucial."