From Longman Dictionary of Contemporary Englishunderhandun‧der‧hand1 /ˌʌndəˈhænd◂ $ ˈʌndərhænd/ (also underhanded /ˌʌndəˈhændɪd $ ˌʌndər-/) adjectiveDISHONESTdishonest and done secretlyThey did it all in such an underhand way.He’s been involved in some underhand dealings.► see thesaurus at dishonest →overhand
underhandunderhand2 adverb American EnglishDSif you throw a ballunderhand, you throw it without moving your arm above your shoulder syn underarm British English
Examples from the Corpus
underhand• But how could he be so ... underhand?• It's underhand, but effective.• The Sox would like to see him throw as well over the top as he does underhand on the move.• Alice thought: Throwing underhand, pathetic! - and this scornrefuelled her.• Webster retrieved the ball and flipped it underhand to Rhodes, who had anchored himself at the plate.From Longman Business Dictionaryunderhandun‧der‧hand /ˌʌndəˈhænd◂ˈʌndərhænd/ adjectivedishonest and done secretlyHe has a reputation for underhand dealings.