Having the combining power (valence) of 3.
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tri·va·lent (')trī-'vā-lənt adj
1) having a chemical valence of three
2) conferring immunity to three different pathogenic strains or species <a \trivalent influenza vaccine>
trivalent n a group of three synapsed homologous chromosomes in meiosis
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tri·va·lent (tri-vaґlənt) 1. having a valence of three. 2. effective against three different entities, as diseases or strains of a pathogen.Medical dictionary. 2011.