un ‧ der ‧ sell /ˌʌndəˈsel $ -ər-/ BrE AmE verb ( past tense and past participle undersold /-ˈsəʊld $ -ˈsoʊld/) [transitive]
1 . to sell goods at a lower price than someone else
2 . to make other people think that someone or something is less good, effective, skilful etc than they really are:
I think he undersold himself at the interview.