approaching vs forthcoming

approaching is a noun but forthcoming is not a noun.

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

As adjectives, approaching and forthcoming are synonyms defined as:

Other synonyms of approaching include coming, upcoming.

approaching (noun)	forthcoming (noun)
the act of drawing spatially closer to something
the temporal property of becoming nearer in time
the event of one object coming closer to another

approaching (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