Ineffective sailor vacates subleases at sea (7)
I believe the answer is:
useless
'ineffective' is the definition.
(associated in meaning)
'sailor vacates subleases at sea' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'vacates' suggests deleting specific letters.
'at sea' is an anagram indicator.
'subleases' with 'ab' removed is 'suleses'.
'suleses' anagrammed gives 'USELESS'.
(Other definitions for useless that I've seen before include "Serving no practical purpose" , "Is Sue less impractical?" , "idle" , "Having no beneficial function" , "Ineffectual" .)