Such as Esperanto is partly built on guesswork (6)
I believe the answer is:
tongue
'such as esperanto' is the definition.
I can't tell whether this defines the answer.
'partly built on guesswork' is the wordplay.
'partly' says the answer is hidden in the clue (part of the clue is used).
'TONGUE' can be found hidden inside 'built on guesswork'.
'is' is the link.
Can you help me to learn more?
(Other definitions for tongue that I've seen before include "Style of speaking; lick" , "Organ of taste" , "Flap under shoelaces" , "For example, Danish" , "Part of shoe or mouth" .)