horseback riding vs sit

horseback riding is a noun but sit is not a noun.

Word	Noun	Adjective	Verb	Adverb
horseback riding	Yes	No	No	No
sit	No	No	Yes	No

horseback riding (noun)	sit (noun)
travel by being carried on horseback
the sport of sitting on the back of a horse while controlling its movements

horseback riding (verb)	sit (verb)
	serve in a specific professional capacity
	be in a position in which one's upper body is largely upright and supported by one's backside
	show to a seat; assign a seat for
	take a seat
	be in session
	sit and travel on the back of animal, usually while controlling its motions
	assume a posture as for artistic purposes
	work or act as a baby-sitter
	be around, often idly or without specific purpose
	be located or situated somewhere