taper vs change form

taper is a noun but change form is not a noun.

Word	Noun	Adjective	Verb	Adverb
taper	Yes	No	Yes	No
change form	No	No	Yes	No

As verbs, change form is a hypernym of taper; that is, change form is a word with a broader meaning than taper:

Other hypernyms of taper include change shape, deform.

taper (noun)	change form (noun)
stick of wax with a wick in the middle
a loosely woven cord (in a candle or oil lamp) that draws fuel by capillary action up into the flame
the property possessed by a shape that narrows toward a point (as a wedge or cone)
a convex shape that narrows toward a point

taper (verb)	change form (verb)
give a point to	assume a different shape or form
diminish gradually