At the start of last month it turned very cold (4)
I believe the answer is:
iced
'very cold' is the definition.
(I've seen this before)
'at the start of last month it turned' is the wordplay.
'at' is a charade indicator (letters next to each other).
'the start of' means to remove the last letter.
'last month' becomes 'dec' (short for December, last month of the year).
'it' becomes 'ci' (I am not sure about this - if you are sure you should believe this answer much more).
'turned' says the letters should be written in reverse.
'dec' with its final letter taken off is 'de'.
'de'+'ci' is 'deci'.
'deci' backwards is 'ICED'.
Can you help me to learn more?
(Other definitions for iced that I've seen before include "Made very cold" , "Frozen - with a sugary topping" , "Dispatched" , "Frosted over" , "reduced number of degrees" .)