Intelligible (5)
I believe the answer is:
lucid
'intelligible' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for lucid that I've seen before include "Easily understood; sane" , "Transparently clear" , "Clearly expressed and altogether rational" , "Clearly presented and easily understood" , "Clearly expressed; sane" .)