cowboy vs adventurer

cowboy and adventurer both are nouns.

Word	Noun	Adjective	Verb	Adverb
cowboy	Yes	No	No	No
adventurer	Yes	No	No	No

As nouns, adventurer is a hypernym of cowboy; that is, adventurer is a word with a broader meaning than cowboy:

cowboy: someone who is reckless or irresponsible (especially in driving vehicles)
adventurer: a person who enjoys taking risks

Other hypernyms of cowboy include venturer.

cowboy (noun)	adventurer (noun)
someone who is reckless or irresponsible (especially in driving vehicles)	a person who enjoys taking risks
a performer who gives exhibitions of riding and roping and bulldogging	someone who travels into little known regions (especially for some scientific purpose)
a male hired hand who tends cattle and performs other duties on horseback