the word 'troth' originates from the old english 'trēowth', which means 'truth, faithfulness, pledge'. this old english term is itself derived from 'trēowe', meaning 'faithful, trustworthy', a cognate of the old norse 'tryggr'. the underlying proto-germanic root is treuwaz, conveying concepts of firmness, trustworthiness, and a binding promise. this root is also the source of the modern english word 'true'. over time, 'troth' evolved from its general meaning of 'truth' to become specialized, referring specifically to the fidelity pledged in a solemn covenant, most famously in the phrase "to plight one's troth" used in marriage vows. its journey reflects a semantic narrowing from a broad concept of truth to a concrete promise of loyalty.

the word is a simplex unit derived from a single old english root. it is not productively formed from separable modern english morphemes.