Inattentive seaman tangled nets (6)
I believe the answer is:
absent
'inattentive' is the definition.
(similar in meaning)
'seaman tangled nets' is the wordplay.
'seaman' becomes 'ab' (short for able seaman).
'tangled' indicates an anagram.
'nets' with letters rearranged gives 'sent'.
'ab'+'sent'='ABSENT'
(Other definitions for absent that I've seen before include "nowhere to be seen" , "elsewhere" , "Not where one should be" , "Not at a specified place" , "Not present - vacuous" .)