Correct spelling

eighth

Correct spelling, explaination: to create ordinal number form from cardinal number we usually add suffix -th to the word. Because of the fact that eight ends with consonant t we just have to add h at the end: eighth. We can’t omit the first h from eight, therefore eigth is a misspelling.

Definition of eighth:
numeral, ordinal number between seventh and ninth
It is my eighth day at new work and I like it very much already.
Jack got a bike for his eighth birthday.


Incorrect spelling

eigth

Incorrect spelling, explaination: eigth is a wrong spelling, because to create an ordinal number in most cases we have to add suffix -th to the cardinal number. This way ordinal number from eight is eighth (we skip the t since it is already there).