tithe

Tithe comes from Old English tēoþa, meaning "tenth," tracing back to a proposed Proto-Germanic root for "a tenth," *tehunþô. Along the way, an Ingvaeonic sound change dropped the nasal consonant that once sat inside the word.

The verb sense (to tithe, meaning to give a tenth) developed in Middle English from the Old English verb tēoþian, built on the same numerical root as the noun.

Tithe is a doublet of tenth — the two words descend from the same Old English root but took different paths into modern English.