Definition of Signature

Signature: 1) That part of the prescription that contains the doctor's directions to the patient. For example, the signature might say "take twice daily with food". Also known as the sig.. 2) The outward appearance of a natural object, which was once taken as a token of its special properties. This ancient doctrine of signatures led some to conclude that the walnut, which looks something like a tiny brain, could be used to heal brain problems; the liverwort plant, which has a three-lobed liver-like leaf, was useful in treating liver disease; and so on. Not too many physicians accept such fanciful ideas today.

The word "signature" comes from the Latin "signare" meaning "to sign or mark."