A stiff drink can be a drink with a high percentage of alcohol.

Stiff also has two uses in professional wrestling:

Stiff, an Australian movie starring David Wenham

Stiff Records, a British record label

Stiff, used to describe how hard a wrestler is attacking his/her opponent

Stiffness, a material's resistance to bending

Stiff differential equation, an equation that exhibits behaviour at two widely different scales (the differential equations describing stiff materials are stiff differential equations)

Stiff: The Curious Lives of Human Cadavers, a book about corpses by Mary Roach

Stiff pattern or Stiff diagram, a method of plotting anion and cation concentrations in meq/L [1]