Frosty means covered in frost, or very cold in manner. A frosty morning, a frosty reception, frosty air.
The weather sense is literal and the human one is a dead metaphor that still works — a frosty reception is polite and unwelcoming at once, which is more chilling than rudeness. A frosty morning is one below freezing, not merely cold.
1adjectivefrostyCovered in frost.
“The car windows were frosty, so he had to scrape them before driving to work.”
2adjectivecoldVery cold in manner.
“When I asked for a pay rise, my boss gave me a frosty look and said nothing.”
frosty is a quality of cold.
Old English forstig, from frost, from a Germanic root meaning to freeze.
Proto-West Germanic
*frostag
Old English
forstiġ
Middle English
frosty
English, today
frosty
Built from
From Middle English frosty, forsty, from Old English forstiġ, fyrstiġ (“frosty”), from Proto-West Germanic frostag, frustīg, by surface analysis, frost + -y. 2 Cognate with West Frisian froastich (“frosty”), Dutch vorstig (“frosty”), German Low German fröstig (“frosty”), German frostig (“frosty”), Swedish frostig (“frosty”). Compare also stq froasterch (“frosty”), German Low German frösterg (“frosty”).
Etymology from Wiktionary, CC BY-SA