keep vs fastness

keep and fastness both are nouns.

Word	Noun	Adjective	Verb	Adverb
keep	Yes	No	Yes	No
fastness	Yes	No	No	No

As nouns, fastness is a hypernym of keep; that is, fastness is a word with a broader meaning than keep:

Other hypernyms of keep include stronghold.

keep (noun)	fastness (noun)
the main tower within the walls of a medieval castle or fortress	a strongly fortified defensive structure
a cell in a jail or prison	a rate (usually rapid) at which something happens
the financial means whereby one lives	the quality of being fixed in place as by some firm attachment

keep (verb)	fastness (verb)
prevent (food) from rotting
prevent the action or expression of
stick to correctly or closely
maintain by writing regular records
supply with necessities and support
hold and prevent from leaving
retain possession of
look after; be the keeper of; have charge of
retain rights to
maintain for use and service
have as a supply
store or keep customarily
stop (someone or something) from doing something or being in a certain state
allow to remain in a place or position or maintain a property or feature
conform one's action or practice to
behave as expected during of holidays or rites
cause to continue in a certain state, position, or activity
supply with room and board
maintain in safety from injury, harm, or danger
fail to spoil or rot
continue a certain state, condition, or activity
to rear