Underwear
An undershirt is an old word for a piece of underwear covering the torso, which has fallen out of usage in the UK, but is still commonly used in North America. Vests is by far the most common term in the UK. Underpants  or pants cover the part of the body where the sex organs are, but never drawers. Most common words: are shorts  as in boxer shorts for the looser fit. Y-fronts for the tight fit (UK), boxers or briefs used for the same things in Canada and the USA.