Measure that requires unusual care (4)
I believe the answer is:
acre
'measure that' is the definition.
'acre' can be an answer for 'measure' (acre is a kind of measure). I'm not certain of the remainder of the definition.
'unusual care' is the wordplay.
'unusual' indicates an anagram.
'care' anagrammed gives 'ACRE'.
'requires' is the link.
Can you help me to learn more?
(Other definitions for acre that I've seen before include "point four nought five of a hectare" , "Square measure of land" , "region of ground" , "Measure of land area" , "Care about this bit of land" .)