A symbolic object that is conventionally used to identify a person or deity.  For example, the attributes of the Greek god Apollo are a lyre and bow; the attribute of the Hindu god Vishnu is a trident; the attribute of St. Catherine of Alexandria is the wheel on which she was martyred.

Caravaggio. St. Catherine of Alexandria. Oil on canvas. 1598. Museo Thyssen-Bornemisza, Madrid.