Real tailor oddly giving proportion (5)
I believe the answer is:
ratio
'proportion' is the definition.
(thesaurus)
'real tailor oddly' is the wordplay.
'oddly' indicates alternate letters.
'real'+'tailor'='realtailor'
The alternate letters of 'realtailor' are 'RATIO'.
'giving' acts as a link.
(Other definitions for ratio that I've seen before include "Proporation, quantitative relation" , "Comparative measure" , "Relationship between two numerical quantities" , "Proportional relation between two numbers" , "Comparative figure" .)