The Trilliant diamond, also known as a Trillion or Trielle™ diamond, is a triangular shaped diamond with 50 facets cut in a brilliant style. The Trielle was developed by Leon Finker in 1978. Prior to 1991, the patented brand name for the Trielle was the Trillion.

Trilliants are often used as side or accent diamonds although they can also be mounted as the central stone for striking effect.

Trilliant diamonds display a very sharp brilliance or fire if the diamond is cut to the correct depth allowing good scintillation.