Surreptitious (7)
'surreptitious' is the definition.
(synonyms)
This is all the clue.
(Other definitions for underhand that I've seen before include "way of delivering service." , "In a secret or dishonest way" , "Crafty" , "Deceitful" , "done deviously through cover" .)
'surreptitious' is the definition.
(I know that surreptitious can be written as furtive)
This is all the clue.
(Other definitions for furtive that I've seen before include "Skulking" , "Surreptitious" , "Clandestine" , "Stealthy; secret" , "Sly, underhand" .)