Old part of the storage depot (4)
I believe the answer is:
aged
'old' is the definition.
(similar in meaning)
'part of the storage depot' is the wordplay.
'part of' says the answer is hidden in the clue.
'AGED' is hidden within 'the storage depot'.
(Other definitions for aged that I've seen before include "well over the hill" , "Mature" , "Like Uncle Arly" , "Long in the tooth" , "Old or ancient" .)