Obtuse

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late Middle English (in obtuse (sense 3)): from Latin obtusus, past participle of obtundere ‘beat against’ (see obtund).

wiktionary

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From Middle French obtus(“obtuse (geometry); narrow-minded, obtuse; boring, dull, lifeless”), from Latin obtūsus(“blunt, dull; obtuse”), past participle of obtundere, from obtundō(“to batter, beat, strike; to blunt, dull”), from ob-(“prefix meaning against”) (see ob-) + tundō(“to beat, strike; to bruise, crush, pound”) (ultimately from Proto-Indo-European *(s)tewd-, from *(s)tew-(“to hit; to push”)). More at obtund.

etymonline

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obtuse (adj.)

early 15c., "dull, blunted, not sharp," from Latin obtusus "blunted, dull," also used figuratively, past participle of obtundere "to beat against, make dull," from ob "in front of; against" (see ob-) + tundere "to beat," from PIE *(s)tud-e- "to beat, strike, push, thrust," from root *(s)teu- "to push, stick, knock, beat" (source also of Latin tudes "hammer," Sanskrit tudati "he thrusts"). Sense of "stupid, not acutely sensitive or perceptive" is by c. 1500. In geometry, in reference to a plane angle greater than a right angle," 1560s. Related: Obtusely; obtuseness.