Design board game with a pound sign (4)
I believe the answer is:
goal
'design' is the definition.
(thesaurus)
'board game with a pound sign' is the wordplay.
'board game' becomes 'go' (go is a kind of board game).
'with' says to put letters next to each other.
'a pound sign' becomes 'al' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'go'+'al'='GOAL'
Can you help me to learn more?
(Other definitions for goal that I've seen before include "Aim and objective" , "Aim (at football)" , "Footballer's target" , "Objective, purpose" , "Football score" .)