- Chess knight
- Knight of (the Order of) the Thistle
- Knight (or Knights) Templar
- Nautical knot (measurement)
Origin of K-TK, short for Cretaceous (used instead of C, because that letter is often used as an abbreviation of Cambrian) + Tertiary.
- (colloquial) Katie (given name)
- Central Kalimantan, a province of Indonesia.