Is “Countermark” a Scrabble word?
Yes
COUNTERMARK
Valid in at least one Scrabble dictionary
Valid in these dictionaries
SOWPODS / CSW
Scrabble UK & International
TWL / NWL
Scrabble North America
Large English Dictionary
General English word list
Meaning of Countermark
noun
1.A mark or token added to those already existing, as a security or proof.
2.An artificial cavity made in the teeth of horses that have outgrown their natural mark, to disguise their age.
verb
1.To apply a countermark to.
“to countermark a horse's teeth”