sack vs send packing

sack is a noun but send packing is not a noun.

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

As verbs, send packing is a hyponym of sack; that is, send packing is a word with a more specific, narrower meaning than sack:

Other hyponyms of sack include retire, pension off, clean out, furlough, lay off, squeeze out, dismiss, drop, send away.

sack (noun)	send packing (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

sack (verb)	send packing (verb)
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