Intellectual, a.
Etymology: [L. intellectualis: cf. F. intellectuel.]
1. Belonging to, or performed by, the intellect; mental; as, intellectual powers, activities, etc. Logic is to teach us the right use of our reason or intellectual powers. I. Watts.
2. Endowed with intellect; having the power of understanding; having capacity for the higher forms of knowledge or thought; characterized by intelligence or mental capacity; as, an intellectual person. Who would lose, Though full of pain, this intellectual being, Those thoughts that wander through eternity Milton.
3. Suitable for exercising the intellect; formed by, and existing for, the intellect alone; perceived by the intellect; as, intellectual employments.
4. Relating to the understanding; treating of the mind; as, intellectual philosophy, sometimes called "mental" philosophy.
1 other Webster entry under this spelling
Intellectual, n.
The intellect or understanding; mental powers or faculties. Her husband, for I view far round, not nigh, Whose higher intellectual more I shun. Milton. I kept her intellectuals in a state of exercise. De Quincey.
Shades of meaning
Fernald has no entry of its own for intellectual; he lists it under clever.
He lists it without comment; the entries above explain its neighbors.