Icy cold, as eels may be, we’re told (5)
I believe the answer is:
gelid
'icy cold' is the definition.
(I've seen this before)
'as eels may be we're told' is the wordplay.
'as eels may be' becomes 'jellied' (as in jellied eels).
'we're told' shows a homophone (sound like).
'jellied' sounds like 'GELID'.
(Other definitions for gelid that I've seen before include "Glacial" , "Extremely cold, frozen" , "Icy cold - glide (anag)" .)