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.