The earliest attested forms of this name occur in Old German, as Haimo.
The form Haimon was then combined with the Anglo-Norman diminutive suffix -et, giving the pet-name Hamunet.
These names come in turn from the Old English words hēah ('high') and tūn ('estate, farmstead', thus meaning 'high farmstead') with the later addition of the Anglo-Norman diminutive suffix -et.
As of around 2011, 116 individuals had the surname Hannett in Great Britain, and none in Ireland.
In 1881, 74 people in Great Britain had the name, being clustered in Lancashire, Lincolnshire, and Nottinghamshire.