Synesthesia: A condition in which the normal separation between the senses appears to have broken down. In synesthesia, sight may mingle with sound, taste with touch, and so on. Females are more often affected than males. People with synesthesia often report that one or more of their family members also had synesthesia, so it may in some cases be an inherited condition. Synesthesia can be induced by certain hallucinogenic drugs and can also occur in some types of seizure disorders.