She's of fundamental importance (4)
I believe the answer is:
dame
'she's' is the definition.
Both the answer and definition are singular nouns.
Maybe they are linked in a way I don't understand?
'of fundamental importance' is the wordplay.
'of' indicates a hidden word.
'DAME' can be found hidden inside 'fundamental importance'.
Can you help me to learn more?
(Other definitions for dame that I've seen before include "Crossdressed panto role" , "Pantomime character" , "Female title; panto part" , "Agatha Christie's title?" , "Man's panto role" .)