Angle of density (6)

I believe the answer is:

obtuse

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'angle' is the definition.
(obtuse angle is a kind of angle)

I don't understand the rest of the clue.

(Other definitions for obtuse that I've seen before include "Slow, dull" , "To be thus blunt" , "Dense, dim about the angle" , "'Dense, slow (6)'" , "A 3dn between 90 and 180 degrees" .)

I've seen this clue in The Globe and Mail.

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