Both instinct and intuition are mental function.

Instinct is the aspect of behavior that is innate. It is complex and normally adaptive. A powerful impulse. An innate aptitude. It is natural and no effort is necessary. You must have heard human instinct. Animal instinct.

Intuition is an intellectual activity or output. It can be stimulated, intensified and enriched during concentration or meditation.

Inference is also another mental function which is used by adepts