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From Biology-Online Dictionary | Biology-Online Dictionary
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(general) Compulsory; restricted to a set of parameters or conditions; having no alternative system or pathway.

(biology) Capable of functioning or surviving only in a particular condition or by assuming a particular behavior.


This descriptive term, which means 'by necessity' is used mostly in biology, such as the following:

Word origin: L obligātus (ptp. of obligāre to bind).

Compare: facultative.