This weapon's found on banks of Calder by seaman (9)
I believe the answer is:
crossword
'this' is the definition.
The definition suggests a singular noun which matches the answer.
'weapon's found on banks of calder by seaman' is the wordplay.
'weapon' becomes 'sword' (sword is a kind of weapon**).
'found on' means one lot of letters go next to another.
'banks of' means to remove the middle letters (the banks are the sides of the word).
'by' says to put letters next to each other.
'seaman' becomes 'os' (I've seen this in other clues).
'calder' with its centre taken out is 'cr'.
'cr'+'os'='cros'
'sword' put after 'cros' is 'CROSSWORD'.
Can you help me to learn more?
(Other definitions for crossword that I've seen before include "See 5" , "One of these, first published December 1913 ..." , "Puzzle (for the intelligent)" , "(Usually) black and white puzzle" , "Letter puzzle" .)