"fellow, lad, man," 1553, rhyming nickname for
Rick, short for
Richard, one of the commonest Eng. names, it has long been a synonym for "fellow," and so most of the slang senses are probably very old, but naturally hard to find in the surviving records. The meaning "penis" is attested from 1891 in British army slang;
dickhead "stupid person" is from 1969. Meaning "detective" is recorded from 1908, perhaps as a shortened variant of
detective. The
Dick Whittington story is an old one, told under other names throughout Europe, of a poor boy who sends a cat he had bought for a penny as his stake in a trading voyage; the captain sells it on his behalf for a fortune to a foreign king whose palace is overrun by rats. The hero devotes part of his windfall to charity, which may be why the legend attached in England since 16c. to Sir Richard Whittington (d.1423), three times Lord Mayor of London, who died childless and devoted large sums in his will to churches, almshouses, and St. Bartholomew's Hospital.