Old dad ultimately upset one's left home (5)
I believe the answer is:
expat
'one's left home' is the definition.
I know nothing about this answer so I cannot tell whether this works.
'old dad ultimately upset' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'dad' becomes 'pa' (both can mean one's father).
'ultimately' says to take the final letters.
The final letter of 'upset' is 't'.
'ex'+'pa'+'t'='EXPAT'
Can you help me to learn more?
(Other definitions for expat that I've seen before include "one settled abroad" , "one working abroad" , "Emigre" , "resident abroad" , "Former countryman" .)