Measure that's confused teacher (7)
I believe the answer is:
hectare
'measure' is the definition.
(hectare is a kind of measure)
'confused teacher' is the wordplay.
'confused' indicates an anagram.
'teacher' with letters rearranged gives 'HECTARE'.
'that's' is the link.
(Other definitions for hectare that I've seen before include "Teacher of metric land measure" , "Some land in France" , "Metric unit of area" , "Metric land area" , "Ten thousand square metres" .)