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protactinium a very toxic radioactive chemical element of the actinide series that has ninety-one protons in each nucleus and that is a product of the radioactive decay of uranium. (symbol: Pa)
protagonist the leading character in a literary work.
protasis in a conditional sentence, the clause that expresses the condition, usu. beginning with "if". (Cf. apodosis.)
protea any flowering shrub from southern Africa of the genus Protea.
protean easily changing form or character; variable or versatile. [2 definitions]
protease any enzyme that stimulates the digestion of protein.
protect to ensure the safety of; shield from danger or harm. [3 definitions]
protectable combined form of protect.
protecting providing security; shielding from danger or harm.
protection the act of protecting or condition of being protected. [4 definitions]
protectionism the theory and practice of imposing high tariffs on imported goods to protect native industries from competition.
protective providing or intending to provide protection.
protector a person who guards against harm or danger; guardian. [2 definitions]
protectorate a smaller, weaker, or less developed country or territory under the protection and partial control of a larger or stronger one.
protégé a person under the care or sponsorship of an influential patron.
protégée a girl or woman under the care or sponsorship of an influential patron.
protein any of a group of complex organic compounds containing nitrogen and composed of chains of amino acids, found in all living organisms and considered essential to all animal life processes.
proteinuria the presence of excess protein in the urine.
pro tem abbreviation of "pro tempore" (Latin); for the time being; temporarily.
pro tempore (Latin) for a time; for the time being; temporarily. [2 definitions]
proteolysis the breaking down of proteins by gastric secretions into simpler, soluble compounds, as in digestion.