Explanation:

- Investigate: This word means to examine or study something systematically. It's commonly used in the context of research or examination.

- Invite: This word refers to asking someone to attend an event or gathering. It's a simple and everyday vocabulary.

- Invent: This word means to create or design something that has not existed before. It's associated with innovation and new ideas.

- involv: This is an incorrect spelling. The correct spelling is involve, which means to include or engage as a part of a whole.

The incorrectly spelt word is:

Option 4: involv