green fingers vs strength

green fingers and strength both are nouns.

Word	Noun	Adjective	Verb	Adverb
green fingers	Yes	No	No	No
strength	Yes	No	No	No

As nouns, strength is a hypernym of green fingers; that is, strength is a word with a broader meaning than green fingers:

Other hypernyms of green fingers include forte, long suit, metier, speciality, specialty, strong point, strong suit.

green fingers (noun)	strength (noun)
a special ability to make plants grow	the property of being physically or mentally strong
	an asset of special worth or utility
	permanence by virtue of the power to resist stress or force
	the amount of energy transmitted (as by acoustic or electromagnetic radiation)
	capability in terms of personnel and materiel that affect the capacity to fight a war
	physical energy or intensity
	capacity to produce strong physiological or chemical effects
	the power to induce the taking of a course of action or the embracing of a point of view by means of argument or entreaty
	the condition of financial success