Fixed look when acquiring last of nail varnish (5)
I believe the answer is:
glaze
'varnish' is the definition.
(thesaurus)
'fixed look when acquiring last of nail' is the wordplay.
'fixed look' becomes 'gaze' (I've seen this before).
'when acquiring' indicates putting letters inside.
'last of' suggests the final letters.
The last letter of 'nail' is 'l'.
'gaze' enclosing 'l' is 'GLAZE'.
(Other definitions for glaze that I've seen before include "Shiny coating" , "become unfocused?" , "Put glass into" , "Fit glass into (windows)" , "Frost" .)