Old criminal carrying a burden (4)
I believe the answer is:
load
'burden' is the definition.
(I know that burden can be written as load)
'old criminal carrying a' is the wordplay.
'criminal' indicates an anagram.
'carrying' means one lot of letters goes inside another.
'old' is an anagram of 'lod'.
'lod' enclosing 'a' is 'LOAD'.
(Other definitions for load that I've seen before include "that's put on commercial vehicle" , "Great quantity" , "Charge a gun" , "Goods carried by a large vehicle" , "Cargo - burden" .)