Definition of phosphorus
2
or less commonly phosphorous \
ˈfäs-f(ə-)rəs
\
: a nonmetallic element of the nitrogen family with atomic number 15 that occurs widely in combination especially as phosphates, that is essential for life in all known organisms, and that is used especially in fertilizers and organophosphorus compounds — see Chemical Elements Table
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Merriam-Webster unabridged
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The first known use of phosphorus was in 1680
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