Learn to speak fluent English -- Accent Training, Correct Grammar usage, Idioms, Phrases and vocabulary with example sentences. When do we really use each one of them? LOSE(v) / OST ( Past participle of Lose) It is a verb form and should be used as a verb in a sentence. Lost is its past tense and past participle. example: I lost my wallet. "Lose some of your weight", mom told her son. LOSS(n) This is a noun form and can be used as a subject, object, or a complement. example. Loss of profit worries him no end. During recession, businessmen incur substantial loss. He was a great loss in the company. LOOSE(adj.) Loose is an adjective and is used to describe something. example: 1. After a month's diet, his jeans became too loose for him . 2. His pet dog is on a loose. (break free) The use of a word is based upon its role in a sentence-how it is used in context. These three are just some of the words that are always used interchangeably without realizing/knowing it.The key is to identify the words function in a sentence and then find out which word fits the role.