Is "freezing fog", a relatively new weather term?

I clearly recall hearing about it in flight training, that was way back in 1995 or so. Said flight training being in the Chicago area. It definitely seems to have been weather jargon of some sort for a long time, but maybe not mainstream.

I might have heard it earlier than that, but the recollection is fuzzy.

Right. The ice fog in Fairbanks gets so dense at -40F (Fairbanks air is very polluted), you literally cannot see beyond your fingertips. Trying to drive a car is pointless, as the ice bounces the light right back at you.

When I was last living in New Zealand, about 10 years ago, “hoar frost” was a common term.

“Freezing fog” has been standard US technical meteorological terminology for decades. I suspect with the advent of the internet and weather channel, a lot more people are being exposed to more details about weather.

40 years ago the local evening TV weather report on the main network channels was “partly cloudy and a high 35 degres, with a chance of snow. Now here’s Dan with the sports.” Big difference vs today.