zero-gradehttp://www.oed.com/dictionary/zero-grade_n%3Ftab%3Dmeaning_and_usezero grade, n.
Revised 2018

zero gradenoun

Linguistics.
  1. 1888–
    The most reduced form of weak ablaut grade, in which the vowel disappears; = nil-grade n.
    1. 1888
      Mors is..in the zero-grade, the Latin -or- representing Indo-European sonant r.
      Academy 11 February 98/3
    2. 1965
      The unfortunate myth that there is some essential connection between aorist aspect and stems consisting of zero-grade root plus accented thematic vowel in Indo-European.
      Language vol. 41 519
    3. 2009
      Lubotsky's equation would require the nonassibilated stop to have been transferred at a late stage from the 0-grade or zero grade.
      Historische Sprachforschung vol. 122 217

Originally published as part of the entry for zero, n. & adj.

zero, n. & adj. was revised in June 2018.