From Longman Dictionary of Contemporary Englishundershortsun‧der‧shorts /ˈʌndəʃɔːts $ ˈʌndərʃɔːrts/ noun [plural] underpants for men or boys
Examples from the Corpus
undershorts• The body of Nichols when found was clad only in undershorts.• Lately, the foundation has cashed in on sales of undershorts.• A few grams can be legitimately shed by stripping to undershorts and T - shirts.• He was wearing undershorts, he remembered that. 