Strange game, mah-jong, to begin with (3)
I believe the answer is:
rum
'strange' is the definition.
(synonyms)
'game mah-jong to begin with' is the wordplay.
'game' becomes 'RU' (rugby union).
'mah-jong' becomes 'm' (this might be a standard abbreviation of which I'm unaware).
'to begin with' says to put letters next to each other.
'ru'+'m'='RUM'
(Other definitions for rum that I've seen before include "Odd like drink distilled from molasses" , "Pirate's grog" , "Eerie" , "Unusual" , "Odd spirit from sugar cane" .)