Solidify, harden (3)
I believe the answer is:
set
This clue is a double definition.
'solidify' is the first definition.
(I know that set is a more specific form of solidify)
'harden' is the second definition.
(set can mean to go hard or dry)
(Other definitions for set that I've seen before include "Solidified" , "Major division of tennis match" , "Gel; group" , "Put down the tennis group" , "(Of the sun) drop below the horizon" .)