Meaning of bis- | Babel Free

Definitions

1. An occasional variant of bi- prefixed to roots beginning with a vowel, as in bisalternate
   morpheme
2. A variant of di- used to indicate that the component that does not take the prefix occurs twice in the compound: a bisoxide is of the form B₂O (cf. dioxide for XO₂)
   morpheme, obsolete
3. A variant of di-, used for substitutions of two complex rather than simple units.
   morpheme

Examples

“Bis (η⁶-arene) metal complexes have been made for many transition metals by the Al/AlCl₃ reduction method.”

CEFR level