retardation vs postponement

retardation and postponement both are nouns.

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

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

Other hypernyms of retardation include delay, hold, time lag, wait.

retardation (noun)	postponement (noun)
the act of slowing down or falling behind	act of putting off to a future time
a decrease in rate of change	time during which some action is awaited
lack of normal development of intellectual capacities
any agent that retards or delays or hinders
the extent to which something is delayed or held back