Cold? It's good to wear a hat (5)

'cold?' is the definition.
('algid' can be similar in meaning to 'cold')

'good to wear a hat' is the wordplay.
'good' becomes 'g' (abbreviation).
'to wear' indicates putting letters inside (to wear something is to be covered up by it).
'hat' becomes 'lid' (lid can informally mean a hat).
'a'+'lid'='alid'
'g' put inside 'alid' is 'ALGID'.

'it's' acts as a link.