Girl filling empty shoes, slippers? (6)
I believe the answer is:
skates
'slippers?' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Maybe there's an association between them I don't understand?
'girl filling empty shoes' is the wordplay.
'girl' becomes 'kate' (**).
'filling' means one lot of letters goes inside another.
'empty' suggests removing the centre.
'shoes' with its middle removed is 'ss'.
'kate' placed inside 'ss' is 'SKATES'.
(Other definitions for skates that I've seen before include "'Sports equipment, with wheels or blades (6)'" , "Tropical Rays" , "Glides along on the big fish?" , "One glides on them, as over ice" , "things to wear on the feet" .)