Guesswork is working something out without the facts to go on. Pure guesswork, take the guesswork out of it, rely on guesswork.
The commonest use is a boast in reverse: a product that takes the guesswork out of something is claiming to supply the missing facts. Educated guesswork is the polite name for the same thing done by somebody who knows the field.
1nounguessworkWorking something out without the facts to go on.
“Without a map, finding the path was pure guesswork.”
guesswork is a guessing.
Guess plus work, on the pattern of handiwork.
From guess + work. Compare Dutch giswerk (“guesswork”).
Etymology from Wiktionary, CC BY-SA