Strong keep, and I don't know why it is thought of as "lame". The term has a particular meaning to the game of chess, i.e. one of the tokens used to play the game and not a timekeeping device, medal, etc.
Also, "chess piece" has more entries in both Google and Google Books than "chesspiece", so I think chesspiece should be just an alt spelling of chess piece. Actually I had never seen the single word spelling "chesspiece" until now! Facts707 10:28, 13 May 2010 (UTC)
"Lameness" is just subjective. It isn't and shouldn't be a formal criterion for excluding. Both "chesspiece" and "chess piece" are compositional and thus lame, IMO. I'm taking a monolingual perspective. Obviously they are relevant for translations. I've added or worked on many a "lame" entry, but prefer to work on others. DCDuringTALK 10:56, 13 May 2010 (UTC)
Well, yes, if chess piece is not significantly more common then WT:COALMINE, q.v., doesn't apply.—msh210℠ 16:28, 13 May 2010 (UTC)