stolid (adj.)

c. 1600, back-formation from stolidity, or else from Middle French stolide (16c.), from Latin stolidus "insensible, dull, slow, brutish, rude, stupid," properly "unmovable," related to stultus "foolish," from PIE *stol-ido-, suffixed form of root *stel- "to put, stand, put in order," with derivatives referring to a standing object or place.