Rhythm to measure about right (5)
I believe the answer is:
metre
'rhythm' is the definition.
(I've seen this in another clue)
'measure about right' is the wordplay.
'measure' becomes 'mete' (meting things out is measuring them out).
'about' indicates putting letters inside.
'right' becomes 'r' (common abbreviation).
'mete' going around 'r' is 'METRE'.
'to' is the link.
(Other definitions for metre that I've seen before include "100cm" , "Distance" , "Characteristic of feet" , "Basic unit of length" , "Poetic rhythm" .)