Tyrant's son entering warehouse (6)
I believe the answer is:
despot
'tyrant's' is the definition.
(synonyms)
'son entering warehouse' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'entering' means one lot of letters goes inside another.
'warehouse' becomes 'depot' (I've seen this before).
's' inserted inside 'depot' is 'DESPOT'.
(Other definitions for despot that I've seen before include "Cruel and oppressive dictator" , "Tyrannical dictator" , "Arbitrary ruler" , "Caesar for one" , "who treats others badly?" .)