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or·tho·phos·phate .ȯr-thə-'fäs-.fāt n a salt or ester of orthophosphoric acid
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or·tho·phos·phate (or″tho-fosґfāt) an anion or salt of orthophosphoric acid or of any of its esters; it is the major intracellular anion. Abbreviated Pi. Called also inorganic phosphate.Medical dictionary. 2011.