undersellun·der·sell /ˌʌndəˈsel-ər-/ verb (past tensepst and past participlepp undersold /-ˈsəʊld-ˈsoʊld/) [transitiveT]1COMMERCE to sell goods etc at a lower price than someone elseWe undersell all our rivals.
They claim never to be undersold (=that nobody sells goods as cheaply as they do).
2COMMERCE to sell something for less than its real valueWhen it was privatized, the water industry was massively undersold.
3MARKETINGto make people think that a product or a person is less good, effective, skilful etc than they really areDon’t undersell yourself at the interview.