despatch vs send off

despatch is a noun but send off is not a noun.

Word	Noun	Adjective	Verb	Adverb
despatch	Yes	No	Yes	No
send off	No	No	Yes	No

As verbs, despatch and send off are synonyms defined as:

Other synonyms of despatch include dispatch.

despatch (noun)	send off (noun)
the act of sending off something
killing a person or animal
the property of being prompt and efficient
an official report (usually sent in haste)

despatch (verb)	send off (verb)
send away towards a designated goal	transfer
	throw, send, or cast forward
	send away towards a designated goal