'guesswork' originates from the combination of the words 'guess' and 'work', where 'guess' meant 'to estimate or suppose' and 'work' referred to 'effort or activity'.

'guess' changed from the Old Norse word 'gissa' and 'work' from the Old English 'weorc', eventually forming the modern English word 'guesswork'.

Initially, it meant 'the act of guessing', and over time it evolved into its current meaning of 'forming an opinion based on incomplete information'.