Dictionary:

MDMA

  (ĕm'dē-ĕm-ā')

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A drug, C₁₁H₁₅NO₂, that is chemically related to amphetamine and mescaline and is used illicitly for its euphoric and hallucinogenic effects. It reduces inhibitions and was formerly used in psychotherapy but has been banned in the United States.

[m(ethylene)d(ioxy)m(eth)a(mphetamine).]

3,4-Methylenedioxymethamphetamine; a mescaline analog.

The noun has one meaning:

Meaning #1: a stimulant drug that is chemically related to mescaline and amphetamine and is used illicitly for its euphoric and hallucinogenic effects; it was formerly used in psychotherapy but in 1985 it was declared illegal in the United States
  Synonyms: methylenedioxymethamphetamine, Adam, ecstasy, X