Lose one's footing on a piece of glass (5)
I believe the answer is:
slide
'glass' is the definition.
(thesaurus)
'lose one's footing on a piece' is the wordplay.
'lose one's footing' becomes 'se' (I am not sure about this - if you are sure you should believe this answer much more).
'on' means one lot of letters goes inside another (as in clothing 'on' a person).
'a piece' becomes 'lid' (lid is a kind of piece).
'se' enclosing 'lid' is 'SLIDE'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for slide that I've seen before include "Playground equipment with sloping surface" , "Slip, slither, skid" , "Trombone part" , "Idles about on children's chute" , "Transparency" .)