Appalling means shockingly bad or horrifying. Appalling conditions, an appalling mistake, absolutely appalling.
It is at the top of the range for disapproval and is used for genuine horror and for weather and service alike, which has worn it down somewhat in British speech. Appalling conditions is the standard phrase in inspection reports. Note appal; and that the word originally meant to grow pale — appalling is literally something that drains the colour from you.
1adjectiveappallingShockingly bad or horrifying.
“The hotel room was appalling: the sheets were dirty and the shower didn't work.”
synonyms: dreadful, shocking
appalling is a quality of shocking badness.
by surface analysis, appall + -ing.
Etymology from Wiktionary, CC BY-SA