A peculiar sect, one cold and austere (7)
I believe the answer is:
ascetic
'austere' is the definition.
('ascetic' can be a synonym of 'austere')
'a peculiar sect one cold' is the wordplay.
'peculiar' indicates anagramming the letters (I've seen this in other clues).
'one' becomes 'i' (Roman numeral).
'cold' becomes 'c' (eg on taps).
'sect' with letters rearranged gives 'scet'.
'a'+'scet'+'i'+'c'='ASCETIC'
'and' acts as a link.
(Other definitions for ascetic that I've seen before include "he never imbibes" , "Religiously self-disciplined" , "Person who practises self-denial as spiritual discipline" , "One practises self-denial as a spiritual discipline" , "reclusive" .)