From The Collaborative International Dictionary of English v.0.48 [gcide]:
four-spot \four-spot\ n.
A playing card or domino or die whose upward face shows four
pips.
[WordNet 1.5]
From WordNet (r) 3.0 (2006) [wn]:
four-spot
n 1: a playing card or domino or die whose upward face shows
four pips [syn: four-spot, four]