The incorrectly spelled word is "explaination." The correct spelling is "explanation," which refers to the act of making something clear or understandable.

Explanation of the other options:

☀ Acquaintance: This word is spelled correctly. It refers to a person known to one, but not a close friend.

☀ Acquisition: This word is spelled correctly. It refers to the act of acquiring or obtaining something.

☀ Aggregate: This word is spelled correctly. It can refer to a whole formed by combining several elements or to the total amount or sum of something.