attach vs hold fast

attach and hold fast both are verbs.

Word	Noun	Adjective	Verb	Adverb
attach	No	No	Yes	No
hold fast	No	No	Yes	No

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

Other hyponyms of attach include agglutinate, implant, fasten, adhere, bind, bond, stick, stick to, spat.

attach (verb)	hold fast (verb)
become attached	stick to firmly
cause to be attached
be attached; be in contact with
take temporary possession of as a security, by legal authority
create social or emotional ties