A jolly woman in navy (6)
I believe the answer is:
armada
'navy' is the definition.
(I've seen this before)
'a jolly woman' is the wordplay.
'jolly' becomes 'rm'.
'woman' becomes 'ada'.
'a'+'rm'+'ada'='ARMADA'
'in' acts as a link.
(Other definitions for armada that I've seen before include "Large number of ships (Spanish?)" , "lot of craft" , "A great fleet - Spain had one" , "The Spanish force" , "Large Spanish fleet" .)