This is the 17652nd most frequent Polish word.
zimnym
"Zimnym" means "cold" (instrumental singular form in Polish).
Here, 'zimnym' is used as an adjective describing 'milk', indicating its temperature.
Piłem herbatę z zimnym mlekiem.
I drank tea with cold milk.
In this sentence, 'zimnym' refers to the adjective describing 'metal', again indicating coldness and used as an instrumental case form.
Dotknąłem zimnym metalem stołu.
I touched the table with cold metal.
This use of 'zimnym' describes the attribute of 'room', showing the environmental temperature and used again in instrumental case.