Liable (3)
'liable' is the definition.
(synonyms)
This is all the clue.
(Other definitions for apt that I've seen before include "Fit, suitable" , "Train" , "Fitting - inclined" , "Suitable; quick to learn" , "Pertinent" .)
'liable' is the definition.
(both can mean having a tendency for something)
This is all the clue.
(Other definitions for prone that I've seen before include "Liable (to suffer) - lying down" , "Lying face down or likely to do something" , "Given" , "Recumbent, likely" , "Lying flat" .)