Difficult to upset (5)
I believe the answer is:
staid
(Other definitions for staid that I've seen before include "Proper; sedate" , "Unadventurous, dull" , "Dully unadventurous" , "Stiff; serious minded" , "composed" .)
I believe the answer is:
staid
(Other definitions for staid that I've seen before include "Proper; sedate" , "Unadventurous, dull" , "Dully unadventurous" , "Stiff; serious minded" , "composed" .)