Not quick in learning, thinking, or understanding; lacking mental acuity; dull, dim. Of the mind or its operations.

Dull, insensitive, stupid, obtuse: said, it appears, originally of the sight, whence of the perceptions generally, and the intellect. (Now…

Characterized by a lack of knowledge or education; not having or showing a high level of mental acuity; intellectually unsophisticated.

Brainless, foolish; senseless, stupid. In later use chiefly in collocation with heartless, and somewhat rare. Of a thing, action, etc.

Foolish, doltish, stupid. Of things or actions. Obsolete.

Of mental faculties or actions, or of persons: Slow (or characterized by slowness) of apprehension; dense, crass, thick-headed; stupid, obtuse…

Of words, actions, ideas, etc.: characterized by or associated with lack of intelligence, perceptiveness, common sense, or good judgement…

figurative. Of the mind: Dulled, made gross. Obsolete.

Of personal qualities, ideas, and other things immaterial: Gross; grossly dull or stupid, ‘dense’.

Of an action, idea, personal quality, etc.: unsophisticated, lacking complexity or nuance; foolish, stupid; (occasionally more positively)…

Of an idea, action, etc. Used ironically or sarcastically: unintelligent, dim-witted; unwise, ill-conceived; unnecessarily innovative; too clever by…

Originally: designating an oversimplified or partial view of something (cf. simpliste, adj.); displaying (extreme) simplicity. Now usually…

Stupid, silly.

(un-, prefix1 affix 1.)

Esp. of a person: stupid, foolish, idiotic; daft.

Stupid; inferior. Now rare.