Clumsy cowboy endlessly on tablet (6)
I believe the answer is:
gauche
'clumsy' is the definition.
(gauche means socially awkward or clumsy)
'cowboy endlessly on tablet' is the wordplay.
'cowboy' becomes 'gaucho' (term for a South American cowboy).
'endlessly' means to remove the last letter.
'on' is a charade indicator (letters next to each other).
'tablet' becomes 'e' (E can mean ecstasy or an ecstasy tablet).
'gaucho' with its final letter removed is 'gauch'.
'gauch'+'e'='GAUCHE'
(Other definitions for gauche that I've seen before include "Like maladroit people" , "Clumsy and unsophisticated" , "Awkward left in France" , "left for Paris" , "'Ill-at-ease, awkward (6)'" .)