Underthing is a word that is not widely used in the English language, yet it has several synonyms that can be used in different contexts. For example, some people may refer to the underthing as an undergarment or underwear, which is a clothing item worn beneath other clothes. Other synonyms include lingerie, intimates, and underclothes, which are used to describe similar items. In addition, words such as undershirt, underpants, and underskirt can also be used depending on the specific garment being referred to. These synonyms are useful for those who want to describe the undergarment in a more specific or detailed manner.