Intense enthusiasm, keen interest, or eager greed in pursuing or desiring something.
From Latin 'aviditas' (eagerness, greed), derived from 'avidus' (eager, greedy), entered English through Old French in the 16th century.
In chemistry and immunology, 'avidity' has a specific meaning: it describes how strongly an antibody clings to an antigen—some antibodies grab on with such avidity that they stick around and protect you for years.
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