Philanthropic scientist born during Christmas (5)
I believe the answer is:
nobel
'philanthropic scientist' is the definition.
(Alfred Nobel)
'born during christmas' is the wordplay.
'born' becomes 'b'.
'during' indicates putting letters inside.
'christmas' becomes 'noel' ('Noel' can be a synonym of 'christmas').
'b' going into 'noel' is 'NOBEL'.
(Other definitions for nobel that I've seen before include "Prize guy" , "and 21 Across: Prestigious international award" , "Swedish philanthropist and inventor of dynamite" , "Dynamite inventor, Prize founder" , "Giver of many prizes" .)