Qualified to give a seaman a bit of a lesson (4)
I believe the answer is:
able
'qualified' is the definition.
(I've seen this before)
'give a seaman a bit of a lesson' is the wordplay.
'give' means one lot of letters go next to another.
'a seaman' becomes 'ab' (short for able seaman).
'a bit of a lesson' becomes 'le' (I am not sure about this - if you are sure you should believe this answer much more).
'ab'+'le' is 'ABLE'.
'to' is the link.
Can you help me to learn more?
(Other definitions for able that I've seen before include "Competent and fit, like sailor" , "With the required capacities" , "Skilled" , "Competent, having ability" , "Competent - sort of seaman" .)