standby vs player

standby and player both are nouns.

Word	Noun	Adjective	Verb	Adverb
standby	Yes	Yes	No	No
player	Yes	No	No	No

As nouns, player is a hypernym of standby; that is, player is a word with a broader meaning than standby:

Other hypernyms of standby include actor, histrion, role player, thespian.

standby (noun)	player (noun)
something that can be relied on when needed	a theatrical performer
an actor able to replace a regular performer when required	a person who participates in or is skilled at some game
	someone who plays a music as a profession
	a person who pursues a number of different social and sexual partners simultaneously
	someone who takes part in an activity

standby (adjective)	player (adjective)
ready for emergency use