keep vs sustain

keep is a noun but sustain is not a noun.

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

As verbs, keep and sustain are synonyms defined as:

Other synonyms of keep include maintain.

As verbs, sustain is a hypernym of keep; that is, sustain is a word with a broader meaning than keep:

keep: allow to remain in a place or position or maintain a property or feature
sustain: lengthen or extend in duration or space

Other hypernyms of keep include keep up, prolong.

keep (noun)	sustain (noun)
the main tower within the walls of a medieval castle or fortress
a cell in a jail or prison
the financial means whereby one lives

keep (verb)	sustain (verb)
prevent (food) from rotting	undergo (as of injuries and illnesses)
prevent the action or expression of	establish or strengthen as with new evidence or facts
stick to correctly or closely	admit as valid
maintain by writing regular records	supply with necessities and support
supply with necessities and support	provide with nourishment
hold and prevent from leaving	be the physical support of; carry the weight of
retain possession of	lengthen or extend in duration or space
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