One prism, fenced off, brings composure (8,2,4)
I believe the answer is:
presence of mind
'composure' is the definition.
The definition and answer can be both human attributes as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'one prism fenced off' is the wordplay.
'off' indicates an anagram.
'one'+'prism'+'fenced'='oneprismfenced'
'oneprismfenced' with letters rearranged gives 'PRESENCE OF MIND'.
'brings' is the link.
Can you help me to learn more?
(Other definitions for presence of mind that I've seen before include "Wits are required to display such" , "alertness in crisis" .)