The word 'vow' entered English in the 13th century from the Anglo-French 'vou' or 'vu', which itself descended from the Latin 'vōtum', meaning 'a promise, dedication, or wish'. This Latin term is the neuter past participle of 'vovēre', meaning 'to promise solemnly, pledge'. The core semantic thread from its ancient root to its modern usage is the concept of a binding, often sacred, verbal commitment. While the religious connotations remain strong, the word has broadened to encompass any solemn or earnest promise, retaining its gravity and sense of personal dedication.

The word 'vow' is a simplex word of Latin origin via Anglo-French. It does not contain separable, productive morphemes in modern English.