Important having special lockers (4)
I believe the answer is:
keys
'lockers' is the definition.
(I've seen this before)
'important having special' is the wordplay.
'important' becomes 'key' (similar in meaning).
'having' means one lot of letters go next to another.
'special' becomes 'S' (common abbreviation as in Special Air Service).
'key'+'s'='KEYS'
(Other definitions for keys that I've seen before include "Bunch of openers?" , "Islands; piano parts" , "Levers on, eg, flute" , "Lock-openers?" , "Lower House of the Isle of Man parliament" .)