The state or quality of being connascent; the fact of growing or originating together, especially of twins or things born at the same time.
From 'connascent' (from Latin 'connascens'—con- 'together' + nascens 'being born') plus the abstract noun suffix '-cy,' creating a noun meaning the condition or quality of being born together.
This is a beautifully precise but archaic medical and philosophical term—doctors and scholars used it to discuss twins or other things originating simultaneously, but modern medicine has mostly replaced it with simpler language!
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