Rest one's dropped in the French river (7)
I believe the answer is:
leisure
'rest' is the definition.
(leisure is a kind of rest)
'one's dropped in the french river' is the wordplay.
'one's' becomes 'i's' (Roman numeral).
'dropped in' means one lot of letters goes inside another.
'the french' becomes 'le' ('the' in French).
'river' becomes 'ure' (river in Yorkshire).
'le'+'ure'='leure'
'is' inserted within 'leure' is 'LEISURE'.
(Other definitions for leisure that I've seen before include "Time available for ease and relaxation" , "may suggest fun and games" , "Free time; relaxation" , "Time for relaxation and pleasure" , "Enjoyment of free time" .)