Became smaller (10)
(Other definitions for contracted that I've seen before include "Got shorter" , "Formally agreed; shrank" .)
'became smaller' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for shrank that I've seen before include "Shrivelled" , "Contracted, grew smaller" , "Reduced in size" , "Became smaller" , "Flinched" .)