D noun 1 LSD us, 1971. 2 Dilaudid, a synthetic opiate US, 1954. 3 narcotics US, 1976. 4 used as a term of address, young man to young man. An abbreviation of DUDE. US, 1997. 5 a police detective US, 2005. 6 a (pre-decimalisation, 1971) penny. From Latin denarius, a rough equivalent of an old penny used in the standard abbreviation for pre-decimal Sterling: £1sd. UK, 1387. 7 in poker, the fourth player to the left of the dealer US, 1988. 8 a demilitarised zone. A shortening of DMZ, the official abbreviation. US, 1991. 9 a member of the Disciples youth gang AUSTRALIA, 1882