We found 2 dictionaries that define the word grade 0:

General (1 matching dictionary)

1. grade 0: Wiktionary

Religion (1 matching dictionary)

2. Scientology® and Dianetics® (No longer online)

Definitions from Wiktionary (grade 0) ▸ noun:  Synonym of zeroth grade ▸ Words similar to grade 0 ▸ Usage examples for grade 0 ▸ Idioms related to grade 0 ▸ Wikipedia articles (New!) ▸ Words that often appear near grade 0 ▸ Rhymes of grade 0 ▸ Invented words related to grade 0