straw man vs effigy

straw man and effigy both are nouns.

Word	Noun	Adjective	Verb	Adverb
straw man	Yes	No	No	No
effigy	Yes	No	No	No

As nouns, effigy is a hypernym of straw man; that is, effigy is a word with a broader meaning than straw man:

straw man: an effigy in the shape of a man to frighten birds away from seeds
effigy: a representation of a person (especially in the form of sculpture)

Other hypernyms of straw man include image, simulacrum.

straw man (noun)	effigy (noun)
an effigy in the shape of a man to frighten birds away from seeds	a representation of a person (especially in the form of sculpture)
a weak or sham argument set up to be easily refuted
a person used as a cover for some questionable activity