Father's heir has one temper (7)
I believe the answer is:
Here is my best explanation:
'temper' is the definition.
'father's heir has one' is the subsidiary indication.
'father's' becomes 'pas' (pa is a kind of father).
'heir' becomes 'son' (I've seen this before).
'has' is an insertion indicator.
'one' becomes 'i' (roman numeral).
'son' going around 'i' is 'sion'.
(Other definitions for passion that I've seen before include "Ardent love", "Ardour, fervour", "Fervent love", "Strong emotion, anger or love", "true love", "A strong emotion", "Strong feeling of intense emotion", "Rage", "Intense enthusiasm for something" and "fire".)