viper vs serpent

viper and serpent both are nouns.

Word	Noun	Adjective	Verb	Adverb
viper	Yes	No	No	No
serpent	Yes	No	No	No

As nouns, serpent is a hypernym of viper; that is, serpent is a word with a broader meaning than viper:

viper: venomous Old World snakes characterized by hollow venom-conducting fangs in the upper jaw
serpent: limbless scaly elongate reptile; some are venomous

Other hypernyms of viper include ophidian, snake.

viper (noun)	serpent (noun)
venomous Old World snakes characterized by hollow venom-conducting fangs in the upper jaw	limbless scaly elongate reptile; some are venomous
	an obsolete bass cornet; resembles a snake
	a firework that moves in serpentine manner when ignited