- next after the twenty-ninth; being the ordinal number for 30.
- being one of 30 equal parts.
- a thirtieth part, especially of one (1/30).
- the thirtieth member of a series.
- (usually prenominal)
- being the ordinal number of thirty in counting order, position, time, etc: often written 30th
- (as noun)the thirtieth of the month
- one of 30 approximately equal parts of something
- (as modifier)a thirtieth part
- the fraction equal to one divided by 30 (1/30)
Middle English threttyth, from Old English þritigoða; see thirty + -th (1). Respelled 16c. to conform to new spelling of thirty.