defer implies a deliberate putting off to a later time.
deferred buying a car until spring
postpone implies an intentional deferring usually to a definite time.
the game is postponed until Saturday
suspend implies temporary stoppage with an added suggestion of waiting until some condition is satisfied.
business will be suspended while repairs are underway
stay often suggests the stopping or checking by an intervening agency or authority.
the governor stayed the execution
Word History
Etymology
Noun (1)
Middle English, from Old English stæg; akin to Old Norse stag stay
Verb (2)
Middle English, from Anglo-French estei-, estai-, stem of ester to stand, stay, from Latin stare — more at stand
Noun (3)
Middle English, from Middle French estaie, of Germanic origin; akin to Middle Dutch stake pole, Middle Low German stak post, stake pole — more at stake
First Known Use
Noun (1)
before the 12th century, in the meaning defined at sense 1