Is “overly” necessary?

Question

Somehow, overly never struck me as a cromulent word. Over is already an adverb. You can write “This sentence is over-long.” Is there really an advantage to writing “This sentence is overly long”?

Is there a context in which overly is right and over is not?

(Edit: already an adverb.)

Answer 1

Overly is an adverb (not an adjective) and is defined as:

adv. To an excessive degree: overly protective

One of the jobs of an adverb is to modify an adjective, which is what it is doing in your sentence, "This sentence is overly long."

Over has many different meanings, but it does not share the meaning that overly has when it is used as an adverb.