Here is the list of all the English words whose definition contains "OS" containing letters A, B, C, D, E, F, H, I, L, M, N, O, P, Q, R, S, T and U grouped by number of letters:
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Lots of Words is a word search engine to search words that match constraints (containing or not containing certain letters, starting or ending letters, and letter patterns).
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Please note: the Wiktionary contains many more words - in particular proper nouns and inflected forms: plurals of nouns and past tense of verbs - than other English language dictionaries such as the Official Scrabble Players Dictionary (OSPD) from Merriam-Webster, the Official Tournament and Club Word List (OTCWL / OWL / TWL) from the National Scrabble Association, and the Collins Scrabble Words used in the UK (about 180,000 words each). LotsOfWords knows 480,000 words.