Dexterous (pronounced either DEK-stuhr-uhs or DEKS-truhs) is the more usual American spelling of the adjective; dextrous is a variant. The related adverb and both related nouns, however, have no variants and are spelled dexterously, dexterity, and dexterousness, respectively. Curiously enough, ambidextrous and ambidextrously are the only Standard spellings of the adjective and adverb, and ambidexterity is the only related noun.
