Learner's definition of PRONE
1 [more prone; most prone] : likely to do, have, or suffer from something — usually + to
They are prone to (making) errors/mistakes. = They are error-prone/mistake-prone. [=they make many errors/mistakes]
Tests showed that the machine is prone to failure/fail.
He is somewhat prone to depression.
People in my family are prone to heart disease.
He is prone to (having) accidents. = He is accident-prone. [=he has many accidents]
an athlete who is injury-prone [=who is often injured]
2 : lying with the front of your body facing downward