Plural of atonic; substances or drugs that lack normal muscle tone or reduce muscle tension.
From atonic (Greek a- 'without' + tonikos 'relating to tone') + -s plural suffix. The term evolved from medical terminology to describe conditions affecting muscle tension.
The prefix 'a-' meaning 'without' appears in hundreds of English words—atypical, asymptomatic, amoral—it's like a linguistic superpower for describing what's missing or absent.
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