Tenth
wiktionary
From Middle English tenth, tenthe. Old English had tēoþa (origin of Modern English tithe), but the force of analogy to the cardinal number "ten" caused Middle English speakers to recreate the regular ordinal and re-insert the nasal consonant. Ultimately from Proto-Germanic *tehundô. Equivalent to ten(numeral) + -th(suffix forming ordinals).
etymonline
tenth (adj., n.)
"next in order after the ninth; an ordinal numeral; being one of ten equal parts into which a whole is regarded as divided;" mid-12c., tenðe; see ten + -th (1). Replacing Old English teoða (West Saxon), teiða (Northumbrian), which is preserved in tithe. Compare Old Saxon tehando, Old Frisian tegotha, Dutch tiende, Old High German zehanto, German zehnte, Gothic taihunda. As a noun from c. 1200.
