Solidify, coalesce (3)
I believe the answer is:
gel
This clue is a double definition.
'solidify' is the first definition.
(I've seen this before)
'coalesce' is the second definition.
(I've seen this in another clue)
(Other definitions for gel that I've seen before include "Take form" , "Thicken" , "Substance to fix hair in place" , "stiffen" , "well-spoken deb?" .)