Incorrect spelling, explanation: the verb admit usually occurs in its past or gerund form, and in such cases, it has the forms admitted and admitting. The -t letter at the end of the word is doubled, however, in the base form, there is only a single -t letter. Many users of English get confused and they spell the base form as admitt, which is wrong.

Correct spelling, explanation: admit is the word of a Latin origin, where it had the form admittere and it had a close meaning to the verb to send. Over the centuries the meaning of the word has changed and today it is a popular English verb, which can be used in both formal and informal contexts.

Definition of admit:
verb – to accept something, often unpleasant; to have the right to enter a place, organization, or a hospital in case of a medical emergency;
You need to admit that it wasn’t a wise decision.
You can admit the party only if you have a formal invitation.
If your country is not a member of the European Union, you can admit the UK only with a valid visa.
Without valid health insurance, you are not allowed to admit this hospital.

Expressions with admit:
Admit is usually followed by the preposition to or ing form:
You need to go to the police and admit to the crime you committed.
She admitted to receiving a huge amount of money from her rich uncle.

Some typical expressions with admit include: admit defeat, admit guilt or admit failure.