'Slough' probably comes from Old English sloh, a slough or mire.
Its origin is not clear, though: the name may refer to sloughs left by rainwater flowing from the Chiltern Hills to the Thames, or instead to sloe bushes growing nearby. The name is first recorded in the 1190s as Slo, then as Sloo in 1336 and Le Slowe in 1437. Slough began as a hamlet in the parish of Upton-cum-Chalvey, whose name it later displaced.