Locks up or nails down (4)
I believe the answer is:
ices
I believe this is a double definition.
'locks up' is the first definition.
(I've seen this in another clue)
'nails down' is the second definition.
(I've seen this in another clue)
(Other definitions for ices that I've seen before include "Cones etc" , "Kills (slang) - sweets" , "Decorates cake with sugar topping" , "Freezes" , "Cold confections" .)