More than one window sticks when installed (9)

I believe the answer is:

casements

'more than one window' is the definition.
(casement is a kind of window)

'sticks when installed' is the wordplay.
'sticks' becomes 'cements' (cement can mean to stick or bond).
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'installed' indicates putting letters inside.
'cements' placed around 'as' is 'CASEMENTS'.

(Another definition for casements that I've seen is " Windows which open on vertical hinges".)

I've seen this clue in The Independent.

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