Ease one into flat and icy liquid (8)
I believe the answer is:
facility
'ease' is the definition.
(I know that facility is a type of effortlessness)
'one into flat and icy liquid' is the wordplay.
'one' becomes 'i' (Roman numeral).
'into' indicates putting letters inside.
'and' means one lot of letters go next to another.
'liquid' indicates anagramming the letters.
'flat' put after 'icy' is 'icyflat'.
'icyflat' with letters rearranged gives 'faclity'.
'i' going into 'faclity' is 'FACILITY'.
(Other definitions for facility that I've seen before include "Aptitude; fluency" , "Talent; ease" , "Ease in performance or action" , "Natural aptitude" , "urban amenity" .)