Compact disc initially seen in error (5)
I believe the answer is:
dense
'compact' is the definition.
(similar in meaning)
'disc initially seen in error' is the wordplay.
'initially' suggests taking the first letters.
'in error' is an anagram indicator.
The first letter of 'disc' is 'd'.
'seen' with letters rearranged gives 'ense'.
'd'+'ense'='DENSE'
(Other definitions for dense that I've seen before include "Thick as undergrowth may be" , "Closely crowded together" , "Stupid; compacted" , "Slow-witted" , "Close-knit" .)