Glasses almost providing sight (9)
I believe the answer is:
spectacle
'sight' is the definition.
(I know that spectacle is a type of sight)
'glasses almost' is the wordplay.
'glasses' becomes 'spectacles' (synonyms).
'almost' means to remove the last letter (almost the whole word is kept).
'spectacles' with its final letter taken away is 'SPECTACLE'.
'providing' acts as a link.
(Other definitions for spectacle that I've seen before include "Picture" , "presentation" , "marvel" , "Wonder" , "sensational event" .)