Thirtieth \Thir"ti*eth\, a. [From Thirty: cf. AS. [thorn]r[=i]tig[=o][eth]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.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Thirtieth \Thir"ti*eth\, n. The quotient of a unit divided by thirty; one of thirty equal parts.

Source: Webster's Revised Unabridged Dictionary (1913)