postponement vs holdup

postponement and holdup both are nouns.

Word	Noun	Adjective	Verb	Adverb
postponement	Yes	No	No	No
holdup	Yes	No	No	No

As nouns, holdup is a hypernym of postponement; that is, holdup is a word with a broader meaning than postponement:

postponement: act of putting off to a future time
holdup: the act of delaying; inactivity resulting in something being put off until a later time

Other hypernyms of postponement include delay.

postponement (noun)	holdup (noun)
act of putting off to a future time	robbery at gunpoint
time during which some action is awaited	the act of delaying; inactivity resulting in something being put off until a later time