What does "underpants" mean?

Underwear covering the genitalia and often buttocks, usually going no higher than the navel.

What is a synonym for "underpants"?

Common synonyms include: briefs, pants, petticoat, skivvies, underclothes, undergarment.

Pronounced //ˈʌndə(ɹ)ˌpænts//.

/ˈʌndə(ɹ)ˌpænts/ noun

noun ·Rare ·Advanced level

Noun

1
Underwear covering the genitalia and often buttocks, usually going no higher than the navel. plural, plural-only
"The Italian fashion of wearing red underpants on December 31 is becoming popular, reputedly to guarantee luck for the new year."
2
an undergarment that covers the body from the waist no further than to the thighs; usually worn next to the skin wordnet

"Please take off all your clothes except your underpants and bra."

From under- + pants.