Loose cover across middle of deck (8)
I believe the answer is:
insecure
'loose' is the definition.
(similar in meaning)
'cover across middle of deck' is the wordplay.
'cover' becomes 'insure' (synonyms).
'across' indicates putting letters inside.
'middle of' means to look at the middle letters.
The middle letters of 'deck' are 'ec'.
'insure' placed around 'ec' is 'INSECURE'.
(Other definitions for insecure that I've seen before include "Sinecure for those lacking in confidence" , "Defenceless" , "(Feeling) unsafe" , "Timid" , "Not safe or confident in oneself" .)