obtuse
ub-TOOSadjMeaning slow to understand or to notice
Memory hook an OBTUSE angle: blunt, not SHARP. Everyone shouts “Surprise!” under a giant banner with Sven’s name on it, and he still asks whose birthday it is: he is being obtuse.
Sven was being obtuse; everyone else had guessed the surprise.
In context Lila hinted a dozen times that she wanted to be left alone, but her brother was obtuse and kept asking her to play, never noticing her sighs.
Similar slow, dense, imperceptive, dull
Opposite sharp, astute, perceptive
From Latin obtusus, “blunt, dull,” from obtundere (to beat against, to blunt).