Give good venting of the spleen? (5)
I believe the answer is:
'give' is the definition.
(to grant someone something is to give them it)
'good venting of the spleen?' is the wordplay.
'good' becomes 'g' (abbreviation).
'venting of the spleen?' becomes 'rant' (venting the spleen means expressing anger).
(Other definitions for grant that I've seen before include "Bestow; bursary" , "Allow (something)" , "Concede, like an American general" , "Greek, a soldier" , "Bestow - Ulysses S. - Cary" .)