insist vs stand fast

insist and stand fast both are verbs.

Word	Noun	Adjective	Verb	Adverb
insist	No	No	Yes	No
stand fast	No	No	Yes	No

As verbs, stand fast is a hyponym of insist; that is, stand fast is a word with a more specific, narrower meaning than insist:

Other hyponyms of insist include hold firm, stand firm, stand pat, assert, asseverate, maintain.

insist (verb)	stand fast (verb)
postulate positively and assertively	refuse to abandon one's opinion or belief
be emphatic or resolute and refuse to budge
beg persistently and urgently