What is the part of speech word Good At?

"Good at" is not a single word but a phrase that functions as a prepositional phrase acting as an adjective.

Here's why:

* Prepositional phrase: It consists of a preposition ("at") followed by its object ("good").

* Adjective: It modifies a noun or pronoun by describing a characteristic or quality.

Example:

"He is good at playing basketball."

Here, "good at" modifies the pronoun "He" and describes his ability in basketball.