attach vs leech onto

attach and leech onto both are verbs.

Word	Noun	Adjective	Verb	Adverb
attach	No	No	Yes	No
leech onto	No	No	Yes	No

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

attach (verb)	leech onto (verb)
become attached	admire boundlessly and follow around
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