sun·block 'sən-.bläk n a preparation (as a lotion) applied to the skin to prevent sunburn (as by physically blocking out ultraviolet radiation) also its active ingredient (as titanium dioxide) compare sunscreen
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sun·block (sunґblok″) a topical protective agent, such as one containing zinc oxide or titanium dioxide, that prevents sunlight from reaching the skin; the term is often used interchangeably with sunscreen.Medical dictionary. 2011.