Primarily, a medicine of a thicker consistence than syrup, prepared with opium. A soft electuary. Electuaries when soft are call opiata. But in modern usage generally,

Any medicine that has the quality of inducing sleep or repose; a narcotic.

That which induces rest or inaction; that which quiets uneasiness. They chose atheism as an opiate.

Inducing sleep; soporiferous; somniferous; narcotic.

Causing rest or inaction.