salary increase vs increment

salary increase and increment both are nouns.

Word	Noun	Adjective	Verb	Adverb
salary increase	Yes	No	No	No
increment	Yes	No	No	No

As nouns, increment is a hypernym of salary increase; that is, increment is a word with a broader meaning than salary increase:

Other hypernyms of salary increase include increase.

salary increase (noun)	increment (noun)
the amount a salary is increased	the amount by which something increases
	a process of becoming larger or longer or more numerous or more important