The Collaborative International Dictionary of English v.0.48:

Anaesthetic \An`[ae]s*thet"ic\, Anesthetic \An`es*thet"ic\
   ([a^]n`[e^]s*th[e^]t"[i^]k), a. (Med.)
   (a) Capable of causing anesthesia; as, an[ae]sthetic agents.
   (b) Characterized by, or connected with, anesthesia; as, an
       an[ae]sthetic effect or operation.
       [1913 Webster + AS] anesthetic

The Collaborative International Dictionary of English v.0.48:

anaesthetic \an`[ae]s*thet"ic\, anesthetic \an`es*thet"ic\--AS,
   n. (Med.)
   A substance which produces anesthesia, as chloroform, ether,
   etc.
   [1913 Webster + AS]