Select the INCORRECTLY spelt word.

The correct answer is Neccessity.

Let's analyze the spelling of each option step-by-step:
1. Neccessity: This spelling is incorrect. The correct spelling is Necessity (with a single 'c' and double 's'). It means the state or fact of being required or indispensable.
2. Perseverance: This is spelt correctly. It refers to persistence in doing something despite difficulty or delay in achieving success.
3. Hierarchy: This is spelt correctly. It refers to a system in which members of an organization or society are ranked according to relative status or authority.
4. Knowledgeable: This is spelt correctly. It means intelligent and well-informed.

Therefore, Neccessity is the incorrectly spelt word.