Imagine barrier getting ready for change (8)
I believe the answer is:
daydream
'imagine' is the definition.
(I know that daydream is a more specific form of the action imagine)
'barrier getting ready for change' is the wordplay.
'barrier' becomes 'dam' (dam is a kind of barrier).
'getting' indicates putting letters inside.
'for change' is an anagram indicator (I've seen this in other clues).
'ready' is an anagram of 'ydrea'.
'dam' enclosing 'ydrea' is 'DAYDREAM'.
(Other definitions for daydream that I've seen before include "An idle diurnal fantasy" , "Diurnal reverie" , "Wool-gather" , "Indulge in a fantasy" , "A pleasant diurnal fantasy" .)