pet sitting vs tending

pet sitting and tending both are nouns.

Word	Noun	Adjective	Verb	Adverb
pet sitting	Yes	No	No	No
tending	Yes	Yes	No	No

As nouns, tending is a hypernym of pet sitting; that is, tending is a word with a broader meaning than pet sitting:

pet sitting: the work of a pet sitter; caring for pets in their own home while their owners are away from home
tending: the work of providing treatment for or attending to someone or something

Other hypernyms of pet sitting include aid, attention, care.

pet sitting (noun)	tending (noun)
the work of a pet sitter; caring for pets in their own home while their owners are away from home	the work of providing treatment for or attending to someone or something

pet sitting (adjective)	tending (adjective)
	(usually followed by `to') naturally disposed toward