Horse, a warm-hearted seaman (4)
I believe the answer is:
arab
'horse' is the definition.
(Arab is an example)
'a warm-hearted seaman' is the wordplay.
'hearted' says to take the centre.
'seaman' becomes 'ab' (short for able seaman).
The central letters of 'warm' are 'ar'.
'ar'+'ab'='ARAB'
(Other definitions for arab that I've seen before include "Saudi, e.g." , "Small, lively breed of horse" , "Saudi, perhaps - breed of horse" , "race" , "Horse of a breed originating in the Middle East" .)