send away vs sack

send away is not a noun while sack is a noun.

Word	Noun	Adjective	Verb	Adverb
send away	No	No	Yes	No
sack	Yes	No	Yes	No

As verbs, send away and sack are synonyms defined as:

send away and sack: terminate the employment of; discharge from an office or position

Other synonyms of send away include can, dismiss, displace, fire, force out, give notice, give the axe, give the sack, terminate.

As verbs, sack is a hypernym of send away; that is, sack is a word with a broader meaning than send away:

send away (noun)	sack (noun)
	the termination of someone's employment (leaving them free to depart)
	the plundering of a place by an army or mob; usually involves destruction and slaughter
	a bag made of paper or plastic for holding customer's purchases
	a loose-fitting dress hanging straight from the shoulders without a waist
	a hanging bed of canvas or rope netting (usually suspended between two trees); swings easily
	a woman's full loose hiplength jacket
	any of various light dry strong white wine from Spain and Canary Islands (including sherry)
	the quantity contained in a sack
	an enclosed space

send away (verb)	sack (verb)
terminate the employment of; discharge from an office or position	put in a sack
stop associating with	plunder (a town) after capture
	make as a net profit
	terminate the employment of; discharge from an office or position