'backstaff' originates from English, specifically the words 'back' + 'staff', where 'back' meant 'rear' (the side opposite the sun when measuring) and 'staff' meant 'rod' or 'stick' (a staff used as an instrument).

'backstaff' was coined in early modern English (late 16th to early 17th century) for the instrument developed and popularized by the navigator John Davis (often called Davis's quadrant); the term describes a 'staff' used with the sun at one's 'back' and became the established name for the device.

Initially, the compound literally described a 'staff used with the sun at the back'; over time it came to refer specifically to the particular navigational instrument (Davis's quadrant) used for measuring solar altitude.