uniting vs coalescency

uniting and coalescency both are nouns.

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

As nouns, coalescency is a hyponym of uniting; that is, coalescency is a word with a more specific, narrower meaning than uniting:

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

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