what is mentholated (menthylated) spirits?

Answer 1

I believe you mean methylated spirits. I have never heard of mentholated spirits.

Methylated spirits is (are?) ethanol which has been rendered toxic or otherwise undrinkable, and in some cases dyed.

Traditionally, the main additive was 10% methanol, which gave rise to its name, but this is not always the case now.

Answer 2

"Spirits" generally refers to alcohol, particularly ethanol, so mentholated would refer to ethanol containing menthol, while methylated would refer to ethanol containing methanol, often used as a denaturant.