2. Verb. (rare) (reduce Reduce) ''by'' one (sixth). ¹
3. Verb. (rare) (reduce Reduce) ''to'' one (sixth). ¹
4. Adjective. (rare) ¹
5. Adjective. (rare physics) sixfold degenerate ¹
6. Noun. (rare spectroscopy) A group of six peaks or lines ¹
¹ Source: wiktionary.com