underhand
adjective /ˌʌndəˈhænd/
  /ˌʌndərˈhænd/
(also less frequent underhanded 
 (disapproving) /ˌʌndəˈhændɪd/
  /ˌʌndərˈhændɪd/
)- secret and dishonest
- I would never have expected her to behave in such an underhand way.
 - I promise you there’s nothing underhand about this agreement.
 
Oxford Collocations DictionaryUnderhand is used with these nouns:- dealings
 - tactic
 
Word OriginOld English in the sense ‘in or into subjection, under control’ (see under-, hand).