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' says to put letters next to each other.
'a seaman' becomes 'ab' (short for able seaman).
'to a silly conclusion' becomes 'ly' (I can't justify this - if you can you should give a lot more credence to this answer).
'ab' put 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" .)