Familiarity with or knowledge of something; the quality of being conversant.
From conversant + -cy (alternate suffix forming nouns, similar to -ance). Both 'conversance' and 'conversancy' emerged in the 17th-18th centuries as ways to nominalize 'conversant'.
'Conversancy' and 'conversance' mean nearly the same thing, showing how English sometimes generated multiple noun forms from single adjectives—over time, one usually wins. In this case, 'conversance' persists while 'conversancy' largely vanished, a quiet linguistic competition.
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