Take precaution against being shocked or heart initially sinking (5)
I believe the answer is:
earth
'take precaution' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'against being shocked or heart initially sinking' is the wordplay.
'heart' can be anagrammed to 'EARTH'.
Though, I'm not clear how this is indicated.
Can you help me to learn more?
(Other definitions for earth that I've seen before include "Fox's or badger's lair" , "It is necessary to clear" , "Solid ground" , "underground shelter" , "Badger's burrow" .)