The adjective 'trig' entered English from the Old Norse word 'tryggr', meaning firm, true, or trustworthy. This Norse term is itself derived from the Proto-Germanic 'trewwjaz', a root related to fidelity and steadfastness, which also gives us the English word 'true'. Over time in English, the core sense of reliability and soundness evolved to describe physical neatness, smartness, and good condition. The unrelated, clipped noun form for 'trigonometry' emerged much later in the 19th century as a piece of school slang.

The word is a simplex of Old Norse origin. It functions as a complete lexical unit.