Dictionary.net

• The posterointernal cusp of an upper molar.

1920 - A dictionary of scientific terms.
By Henderson, I. F.; Henderson, W. D.

• [Greek] Postero-internal cusp of upper molar; the part posterior to girdle in Dinoflagellata, opp. epicone.

1920 - A dictionary of scientific terms (6th edition)
By J.H. Kenneth