Question

Is the italicized word in the sentence below an adverb or preposition? Why don't you come over this evening (over)

Answer 1

The italicized word OVER can be used either as a preposition or as an adverb in a sentence. In this particular sentence, the correct answer is adverb.
When over is used as an adverb, it is not followed by any word which would create a phrase along with it (as is the case here). Compare OVER as a preposition (A bird flew over the lake - we can see over what) and OVER as an adverb (Could you come over - we don't know over where or what). 

Answer 2

Answer:

Adverb

Explanation:

Although the word "over" can be used either way it is used as an adverb in this sentence because an adverb modifies a adjective, verb, or another adverb.

Hope this helps.