Formerly acting president (6)
I believe the answer is:
reagan
This might be a double definition.
'formerly acting' is the first definition.
The definition suggests a singular noun which matches the answer.
'president' is the second definition.
(Ronald Reagan)
Can you help me to learn more?
(Other definitions for reagan that I've seen before include "Ronald . . . . . ., 40th president of USA" , "Western star" , "political leader" , "A range for the US President" , "Ronald ..., ex-president of USA" .)