beachhead vs achievement

beachhead and achievement both are nouns.

Word	Noun	Adjective	Verb	Adverb
beachhead	Yes	No	No	No
achievement	Yes	No	No	No

As nouns, achievement is a hypernym of beachhead; that is, achievement is a word with a broader meaning than beachhead:

beachhead: an initial accomplishment that opens the way for further developments
achievement: the action of accomplishing something

Other hypernyms of beachhead include accomplishment.

beachhead (noun)	achievement (noun)
an initial accomplishment that opens the way for further developments	the action of accomplishing something
a bridgehead on the enemy's shoreline seized by an amphibious operation