This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. Alternation of sounds within a word that indicates grammatical information (often inflectional).

n. Vowel-gradation; the vowel-differentiation of words known as ablaut (which see).

gradation    ablaut    mutation    stem    consonant