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"tending to produce sleep," 1680s, from French soporifique (17c.), formed in French from Latin sopor (genitive soporis) "deep sleep" (see sopor). As a noun from 1722. Earlier as an adjective was soporiferous (1580s as "characterized by excessive sleep," c.1600 as "soporific").
soporific sop·o·rif·ic (sŏp'ə-rĭf'ĭk, sō'pə-)
Inducing or tending to induce sleep.