viper vs ophidian

viper and ophidian both are nouns.

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

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

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

Other hypernyms of viper include serpent, snake.

viper (noun)	ophidian (noun)
venomous Old World snakes characterized by hollow venom-conducting fangs in the upper jaw	limbless scaly elongate reptile; some are venomous