A general greeting and welcome to all of our recent newcomers; tickled to have you!

My thought is that defrost is like dial: it harks back to what had to be done in the past. Things in the freezer (including the freezer itself) got covered with frost and had to literally be defrosted; just as phones could only be dialed. Though we still use both words, the actuality of their meanings is getting harder and harder to find.