While the Thai word “Sak” means “to tap”, the Thai word Yant, derived from the Sanskrit word Yantra, which means instrument. A Yantra could be many things, for example, a sacred geometrical design, spell, or chanting that possesses magical powers.
So “Sak Yant” means “to tap out a Yant” or “to hand poke a tattoo” as it is often referred to.
A Yant is a sacred geometric design that includes ancient scriptures that are said to invoke spiritual and magical powers. Yants were in existence long before being tattooed on the skin, often they would be scribed onto a piece of cloth (Pha Yant) and displayed in the home, or rolled up in a small glass tube (Takrut) and worn around the neck.
Another popular method of bearing a Yant was to wear a shirt with the Yant inscribed. Soldiers favored this and went into battle wearing Yant vests (Seu Yant).