sinister vs forbidding

sinister is not a noun while forbidding is a noun.

Word	Noun	Adjective	Verb	Adverb
sinister	No	Yes	No	No
forbidding	Yes	Yes	No	No

As adjectives, sinister and forbidding are synonyms defined as:

sinister and forbidding: threatening or foreshadowing evil or tragic developments

Other synonyms of sinister include baleful, menacing, minacious, minatory, ominous, threatening.

sinister (noun)	forbidding (noun)
	an official prohibition or edict against something

sinister (adjective)	forbidding (adjective)
threatening or foreshadowing evil or tragic developments	threatening or foreshadowing evil or tragic developments
stemming from evil characteristics or forces; wicked or dishonorable	harshly uninviting or formidable in manner or appearance
on or starting from the wearer's left