step in vs supplant

step in and supplant both are verbs.

Word	Noun	Adjective	Verb	Adverb
step in	No	No	Yes	No
supplant	No	No	Yes	No

As verbs, supplant is a hypernym of step in; that is, supplant is a word with a broader meaning than step in:

Other hypernyms of step in include replace, supersede, supervene upon.

step in (verb)	supplant (verb)
get involved, so as to alter or hinder an action, or through force or threat of force	take the place or move into the position of
act as a substitute