Bravery of old university rector put in prison (7)
I believe the answer is:
courage
'bravery' is the definition.
('courage' can be a synonym of 'bravery')
'old university rector put in prison' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'university' becomes 'u'.
'rector' becomes 'r'.
'put in' is an insertion indicator.
'prison' becomes 'cage' (I've seen this before**).
'o'+'u'+'r'='our'
'our' put into 'cage' is 'COURAGE'.
'of' is the link.
(Other definitions for courage that I've seen before include "Bottle" , "Grit" , "See 6" , "Bravery, pluck" , "Daring" .)