Terminology
In the United Kingdom and Ireland most people use trousers or slacks. Pants is used interchangeably with trousers in some northern dialects of England as is kecks . In Scotland, trousers are occasionally known as trews, which is the historic root of the word 'trousers'. Trousers are also known as breeks in Scots. The item of clothing worn under trousers is underpants. The standard form 'trousers' is also used, but it is sometimes pronounced in a manner approximately represented by "tru:zɨrz", which is possibly a throwback to the Gaelic word truis which the English word originates from. In North America and Australia pants is the general category term, whereas trousers (sometimes slacks in Australia and the United States) often refer more specifically to tailored garments with a waistband, belt-loops, and a fly-front. So informal elastic-waist knitted garments would be called pants, but not trousers (or slacks).
North Americans call undergarments underwear, underpants, undies, jockey shorts, shorts, 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 underwear also has various informal terms including under-dacks, undies, 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: Pair Of Pants