Cleverly leading a seaman to a silly conclusion (4)
I believe the answer is:
ably
'cleverly' is the definition.
(thesaurus)
'leading a seaman to a silly conclusion' is the wordplay.
'leading' means one lot of letters go next to another.
'a seaman' becomes 'ab'.
'to a silly conclusion' becomes 'ly' (I can't explain this - if you can you should give a lot more credence to this answer).
'ab' next to 'ly' is 'ABLY'.
Can you help me to learn more?
(Other definitions for ably that I've seen before include "With competence" , "In a competent fashion" , "well" , "In proficient manner" , "With great skill" .)