Thir"ti*eth (?), a. [From Thirty: cf. AS. þritigo&edh;a.]
1.
Next in order after the twenty-ninth; the tenth after the twentieth; -- the ordinal of thirty; as, the thirtieth day of the month.
2.
Constituting or being one of thirty equal parts into which anything is divided.
© Webster 1913.
Thir"ti*eth, n.
The quotient of a unit divided by thirty; one of thirty equal parts.
© Webster 1913.