Terminology
In the United Kingdom, England, and Ireland most people use trousers or slacks as the general category term, whereas pants usually refers to underwear but is used, interchangeably with trousers, in some northern dialects. In Scotland, trousers are known as trews, which is the historic root of the word 'trousers'. Trousers are known as breeks in Scots. The item of clothing worn under trousers is underpants. In North America pants is the general category term, whereas trousers (sometimes slacks in Australia and the United States) often refer more precisely to tailored garments with a waistband, belt-loops, and a fly-front. For instance, informal elastic-waist knitted garments would be called pants, but not slacks.
North Americans call undergarments underwear, underpants, "long johns" or panties (the last are women's garments specifically) to distinguish them from other pants that are worn on the outside. The term drawers normally refers to undergarments, but in some dialects, may be found as a synonym for "breeches", that is, trousers. In these dialects, the term underdrawers is used for undergarments. In Australia, men's undergarments are called underwear, underpants, undies, under-dacks, dacks or jocks.
Various people in the fashion industry use the words trouser or pant instead of trousers or pants. This is nonstandard usage. The words "trousers" and "pants" are pluralia tantum, nouns that generally only appear in plural form—much like the words "scissors" and "tongs". However, the singular form is used in some compound words, such as trouser-leg, trouser-press and trouser-bottoms.
Read more about this topic: Trousers