A nautical lad will provide that extra piquancy (6)
I believe the answer is:
season
'will provide that extra piquancy' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'a nautical lad' is the wordplay.
'a nautical' becomes 'sea' (I can't explain this - if you can you should believe this answer much more).
'lad' becomes 'son' (lad can informally mean a young boy).
'sea'+'son'='SEASON'
Can you help me to learn more?
(Other definitions for season that I've seen before include "Add taste to; part of year" , "Period of a year" , "make things palatable" , "Quarter of the year" , "Particular time (for activity, conditions etc)" .)