What is definition of the word permit?

Depends how you use it. You could be using it as a noun, verb, etc. it can be any of these:

1. to allow to do something: Permit me to explain.

2. to allow to be done or occur: The law does not permit the sale of such drugs.

3. to tolerate; agree to: a law permitting Roman Catholicism in England.

4. to afford opportunity for, or admit of: vents to permit the escape of gases.

5. to grant permission; allow liberty to do something.

6. to afford opportunity or possibility: Write when time permits.

7. to allow or admit (usually fol. by of ): statements that permit of no denial.

8. an authoritative or official certificate of permission; license: a fishing permit.

9. a written order granting special permission to do something.