ἀμβλυγώνιον
From LSJ
μὴ ἐν πολλοῖς ὀλίγα λέγε, ἀλλ΄ ἐν ὀλίγοις πολλά → don't say little in many words, but much in a few words (Stobaeus quoting Pythagoras)
English (LSJ)
τό, obtuse angle, Plb. 34.6.7.
Russian (Dvoretsky)
ἀμβλῠγώνιον: τό тупой угол или тупоугольник Polyb.