Oblong area for games with mat (9)
I believe the answer is:
rectangle
'oblong' is the definition.
(I've seen this before)
'area for games with mat' is the wordplay.
'area for games' becomes 'rec' (I can't explain this - if you can you should give a lot more credence to this answer).
'with' says to put letters next to each other.
'mat' becomes 'tangle' (synonyms).
'rec'+'tangle'='RECTANGLE'
Can you help me to learn more?
(Other definitions for rectangle that I've seen before include "regular sort of figure" , "Four-sided figure" , "Figure on plane" , "Parallelogram with four right angles" , "Geometric figure with four right angles, not square" .)