High up and Overhead

High up adverb - At a great altitude.

Overhead and high up are semantically related In some cases you can use "Overhead" instead the phrase "High up" as an adverb or an adjective or a noun.

Overhead adverb - To or in a higher place.

High up and overhead are semantically related in above topic. Sometimes you can use "High up" instead the word "Overhead" as an adverb or an adjective or a noun.