Comments:АПиПЯЯ 284. See TMN 2, 596-601 (with a hopeless confusion of Turk. *top 'round thing', *toprak 'earth, dust' and *topɨk 'knee cap' - all of which have different etymologies). Cf. also *t`obú 'fruit, cone' (a different root, but a source of some contaminations).