The term originated from the occasional black sheep which are born into a flock of white sheep due to a genetic process of recessive traits. Black wool was considered commercially undesirable because it could not be dyed. In 18th and 19th century England, the black color of the sheep was seen as the mark of the devil.
The transom is the flat back end of a boat. Some boats are pointed on both ends, so they have no transom. A traditional canoe, pointed on both ends has no transom. A modern square stern canoe (made to take an outboard motor) has a transom.
Definition of loom. 1  intransitive verb. 2  1 : to come into sight in enlarged or distorted and indistinct form often as a result of atmospheric conditions Storm clouds loomed on the horizon. 3  2a : to appear in an impressively great or exaggerated form deficits loomed largeb : to take shape as an impending occurrence the problems that loomed ahead.