Shown how tense it can be in hearing (6)
I believe the answer is:
taught
'shown' is the definition.
(shown how to do something)
'how tense it can be in hearing' is the wordplay.
'how tense it can be' becomes 'taut' (taut means tense or tight).
'in hearing' shows a homophone (sound like).
'taut' is a homophone of 'TAUGHT'.
(Other definitions for taught that I've seen before include "Gave instruction" , "as a pupil" , "Educated" , "Tutored" , "Was a teacher" .)