penalty vs amercement

penalty and amercement both are nouns.

Word	Noun	Adjective	Verb	Adverb
penalty	Yes	No	No	No
amercement	Yes	No	No	No

As nouns, amercement is a hyponym of penalty; that is, amercement is a word with a more specific, narrower meaning than penalty:

Other hyponyms of penalty include requital, retribution, forfeit, forfeiture, fine, mulct.

penalty (noun)	amercement (noun)
the act of punishing, or the infliction of a penalty	money extracted as a penalty
the disadvantage or painful consequences of an action or condition
(games) a handicap or disadvantage that is imposed on a competitor (or a team) for an infraction of the rules of the game
a payment required for not fulfilling a contract