piggyback vs modify

piggyback is a noun but modify is not a noun.

Word	Noun	Adjective	Verb	Adverb
piggyback	Yes	No	Yes	Yes
modify	No	No	Yes	No

As verbs, modify is a hypernym of piggyback; that is, modify is a word with a broader meaning than piggyback:

Other hypernyms of piggyback include alter, change.

piggyback (noun)	modify (noun)
the act of carrying something piggyback

piggyback (verb)	modify (verb)
bring into alignment with	make less severe or harsh or extreme
support on the back and shoulders	add a modifier to a constituent
haul by railroad car	cause to change; make different; cause a transformation
haul truck trailers loaded with commodities on railroad cars
ride on someone's shoulders or back

piggyback (adverb)	modify (adverb)
on the back or shoulder or astraddle on the hip
on a railroad flatcar