skiing vs ski jumping

skiing and ski jumping both are nouns.

Word	Noun	Adjective	Verb	Adverb
skiing	Yes	No	No	No
ski jumping	Yes	No	No	No

As nouns, ski jumping is a hyponym of skiing; that is, ski jumping is a word with a more specific, narrower meaning than skiing:

skiing: a sport in which participants must travel on skis
ski jumping: the act of performing a jump on skis from a high ramp overhanging a snow covered slope

Other hyponyms of skiing include cross-country skiing.

skiing (noun)	ski jumping (noun)
a sport in which participants must travel on skis	the act of performing a jump on skis from a high ramp overhanging a snow covered slope