paraphenylenediamine
noun
para·phen·yl·ene·di·amine
| \ -ˌfen-ᵊl-ˌēn-ˈdī-ə-ˌmēn
\
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Medical Definition of paraphenylenediamine
: the para isomer of phenylenediamine that is used especially in dyeing hair and sometimes causes an allergic reaction