William Humphreys Dayas (12 September 1863,^[1] New York – 3 May 1903, Manchester) was an American pianist, pedagogue and composer, one of the last pupils of Franz Liszt. Dayas lost his parents at an early age. He studied organ and composition and moved to Germany in 1881. After studies with Liszt, he taught at European conservatoires, including Helsinki (1890–1893), where his daughter, the pianist and pedagogue Karin Dayas (1892–1971) was born. After that he worked as a piano teacher in Germany, New York and finally as a professor at Royal Manchester College of Music. He composed piano pieces.

William Dayas was married to Margaret (Margarethe) Vocke, a pupil of Liszt, in 1891.^[2]