They have an intimate relationship.

A complete intransitive verb takes neither complement nor object.

The patient received intravenous medication.

I don't like it when people intrude on my personal space.

The security system detected an intruder in the building.

He was accused of intrusion upon her privacy.

The laws of physics are invariable.

She is invariably late for meetings.

Thomas Edison is a famous inventor.

Use an inverted comma at the beginning and end of a direct quote.