call-back vs employment

call-back and employment both are nouns.

Word	Noun	Adjective	Verb	Adverb
call-back	Yes	No	No	No
employment	Yes	No	No	No

As nouns, employment is a hypernym of call-back; that is, employment is a word with a broader meaning than call-back:

Other hypernyms of call-back include engagement.

call-back (noun)	employment (noun)
the recall of an employee after a layoff	the occupation for which you are paid
a return call	the act of using
	the act of giving someone a job
	the state of being employed or having a job