coalescence vs uniting

coalescence and uniting both are nouns.

Word	Noun	Adjective	Verb	Adverb
coalescence	Yes	No	No	No
uniting	Yes	No	No	No

As nouns, uniting is a hypernym of coalescence; that is, uniting is a word with a broader meaning than coalescence:

coalescence: the union of diverse things into one body or form or group; the growing together of parts
uniting: the act of making or becoming a single unit

Other hypernyms of coalescence include conjugation, jointure, unification, union.

coalescence (noun)	uniting (noun)
the union of diverse things into one body or form or group; the growing together of parts	the act of making or becoming a single unit
	the combination of two or more commercial companies