Spot on a domino or die (3)
I believe the answer is:
pip
This clue is a double definition.
'spot on a domino' is the first definition.
(I've seen this in another clue)
'die' is the second definition.
(thesaurus)
(Other definitions for pip that I've seen before include "Spot (on card); seed (of fruit)" , "Palindromic pear seed" , "Greenwich time signal" , "one signals lieutenant" , "Defeat at the last moment - . . . at the post" .)