Explorer sailor in bed (5)
I believe the answer is:
cabot
'explorer' is the definition.
(I've seen this before)
'sailor in bed' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'in' is an insertion indicator.
'bed' becomes 'cot' (cot is a type of bed).
'ab' inserted within 'cot' is 'CABOT'.
(Other definitions for cabot that I've seen before include "Italian leader of the 1497 English expedition to the east coast of today's Canada" , "Sebastian & John -, early navigators" , "John (Giovanni) -, navigator, explored N. America" , "Italian explorer (father or son)" , "Sebastian -, navigator" .)