The half that's better if we go outside! (4)
I believe the answer is:
wife
'the half' is the definition.
(I have seen 'Better half' mean 'wife' so perhaps 'half' could also mean 'wife')
'better if we go outside' is the wordplay.
'if we' anagrams to 'WIFE'.
But, I am unsure how the anagram is indicated.
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for wife that I've seen before include "Better half" , "Hubby's other half" , "Dutch (slang)" , "Partner in marriage" , "Married woman" .)