Sound feeble for seven days (4)
I believe the answer is:
week
'seven days' is the definition.
(I've seen this before)
'sound feeble' is the wordplay.
'sound' shows a homophone (sound like).
'feeble' becomes 'weak' ('weak' can be similar in meaning to 'feeble').
'weak' is a homophone of 'WEEK'.
'for' acts as a link.
(Other definitions for week that I've seen before include "Part of the year" , "Seven days" , "Seven day period" , "Period of time; sounds like feeble" , "A long time in politics?" .)