Memory rocky at first in the morning (3)
I believe the answer is:
ram
'memory' is the definition.
(Random Access Memory on a computer)
'rocky at first in the morning' is the wordplay.
'at first' suggests taking the first letters.
'in the morning' becomes 'am' (AM on a clock).
The first letter of 'rocky' is 'r'.
'r'+'am'='RAM'
(Other definitions for ram that I've seen before include "what comes after fish" , "Animal to batter" , "Prepare to raid" , "Drive hard" , "Object to batter with" .)