foothold vs beachhead

foothold and beachhead both are nouns.

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

As nouns, foothold and beachhead are synonyms defined as:

foothold and beachhead: an initial accomplishment that opens the way for further developments

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

foothold: an area in hostile territory that has been captured and is held awaiting further troops and supplies
beachhead: a bridgehead on the enemy's shoreline seized by an amphibious operation

Other hyponyms of foothold include airhead.

foothold (noun)	beachhead (noun)
an initial accomplishment that opens the way for further developments	an initial accomplishment that opens the way for further developments
a place providing support for the foot in standing or climbing	a bridgehead on the enemy's shoreline seized by an amphibious operation
an area in hostile territory that has been captured and is held awaiting further troops and supplies