coming vs forthcoming

coming is a noun but forthcoming is not a noun.

Word	Noun	Adjective	Verb	Adverb
coming	Yes	Yes	No	No
forthcoming	No	Yes	No	No

As adjectives, coming and forthcoming are synonyms defined as:

Other synonyms of coming include approaching, upcoming.

coming (noun)	forthcoming (noun)
the moment of most intense pleasure in sexual intercourse
arrival that has been awaited (especially of something momentous)
the act of drawing spatially closer to something
the temporal property of becoming nearer in time

coming (adjective)	forthcoming (adjective)
of the relatively near future	available when required or as promised
	of the relatively near future
	at ease in talking to others