Left one cold object - that's allowed (5)
I believe the answer is:
licit
'that's allowed' is the definition.
(I've seen this before)
'left one cold object' is the wordplay.
'left' becomes 'l' (common abbreviation).
'one' becomes 'I' (Roman numeral).
'cold' becomes 'c' (eg on taps).
'object' becomes 'it' (pronoun for an inanimate object).
'l'+'i'+'c'+'it'='LICIT'
(Other definitions for licit that I've seen before include "OK?" , "Legal" , "Acceptable" , "in order" , "Within the law" .)