The term BLACK DUCK can be broken down into four crossword solutions: SMEW (4 letters), EIDER (5 letters), OBOE (4 letters), and SONIA (5 letters). The SMEW is a small duck found in Eurasia and North America, with a distinctive black and white plumage. The EIDER is a large sea duck that breeds in the Arctic regions of Europe, Asia, and North America. The OBOE is a woodwind instrument with a double reed and a conical bore. Finally, SONIA is a female given name of Latin origin, meaning 'WISDOM'.