Obtuse means slow to understand, or blunt in angle. Deliberately obtuse, an obtuse angle, being obtuse about it.
The insult usually comes with deliberately in front, since accusing somebody of being deliberately obtuse says they understood and pretended not to. In geometry an obtuse angle is one greater than ninety degrees.
1adjectiveobtuseSlow to understand, or blunt in angle.
“Am I being obtuse, or does this plan make no sense at all?”
obtuse is a quality.
Latin obtusus means blunted, from obtundere, to beat against or dull.
Proto-Indo-European
*(s)tewd-
Latin
obtūsus — blunt, dull; obtuse
Middle English
obtuse
English, today
obtuse
Built from
From Middle English obtuse, from Latin obtūsus (“blunt, dull; obtuse”), past participle of obtundere, from obtundō (“to batter, beat, strike; to blunt, dull”), from ob- (“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.
Etymology from Wiktionary, CC BY-SA