Correct spelling, explanation: 10th is an ordinal number that comes between 9th and 11th. As all the ordinal numbers – except 1st, 2nd, and 3rd – it’s formed by adding the -th ending, which gives the correct form 10th.

Definition of 10th:
1. number (ordinal) – it comes after 9th and before 11th,
He finished the race in 10th position, which was a great success, taking into consideration the fact that he came back after a serious injury.

Phrases with 10th:
1. one-10th – only one part of something (one out of ten),
I possess this land in one-10th only, which in reality is as if I didn’t possess it at all.

Incorrect spelling, explanation: a popular mistake is to form the ordinal number 10th as 10st. The latter form is incorrect and it is the consequence of the fact the -st ending is added to number one, which gives 1st. Some English users think that the same happens with ten, but in the case of this number, the only correct form is 10th.

Incorrect spelling

Incorrect spelling