This is the 4746th most frequent German word.
zehnten
"Tenth" (ordinal number) or "tithe" (historically, one-tenth portion).
In this instance, 'zehnten' is describing the specific part (tenth) of something distributed.
Ich habe ihm den zehnten Teil gegeben.
I gave him the tenth part.
In this sentence, 'zehnten' is used as an ordinal number to specify the date (tenth day).
Ich treffe dich am zehnten August.
I will meet you on the tenth of August.
Here, 'zehnten' functions as an adjective describing which attempt (ordinal number).