facultative
C2CEFR level
90/100Rarity: very rare
TechnicalRegister
Medicine adjective
Able to live under more than one set of conditions, as with or without oxygen.
Escherichia coli is a facultative anaerobe, thriving whether or not oxygen is available.
Business adjective
Describing reinsurance negotiated separately for a single, individual risk rather than automatically under a treaty.
The unusually large refinery was placed on a facultative basis because it fell outside the treaty terms.
Rarity runs from 0 (a word everyone knows) to 100 (almost never seen outside specialist or literary writing). Level is the word's real difficulty on the CEFR scale, from A1 to C2.
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