Faculty I mention in speech (8)
I believe the answer is:
eyesight
'faculty' is the definition.
(eyesight is a kind of faculty)
'i mention in speech' is the wordplay.
'i' becomes 'eye' (I've seen this in other clues).
'mention' becomes 'cite' (to cite is to mention or quote).
'in speech' shows a homophone (sound like).
'cite' is a homophone of 'sight'.
'eye'+'sight'='EYESIGHT'
(Other definitions for eyesight that I've seen before include "Perceptive faculty" , "Power of vision" , "Ability to see" , "quality of viewing" , "Seeing ability" .)