Hellish means extremely unpleasant. Far worse than bad, and said with feeling.
It is an intensifier drawn from hell, and English has a whole set of these — a hellish journey, a hellish week, hellish traffic. The word is informal and mildly strong, so it suits complaint rather than formal writing. It can also mean literally to do with hell, though that use is rare outside religious writing. As an adverb it appears in British speech as hellishly, meaning extremely.
1adjectivehellishExtremely unpleasant or difficult.
“The drive back was absolutely hellish.”
Also accepted in games: horrid
Middle English
helle
English
hell
English, today
hellish
From hell + -ish. hell comes from Middle English helle. From Middle English hel, hell, helle, hælle, from Old English hel, hell, from Proto-West Germanic hallju, from Proto-Germanic haljō (“hell, netherworld”), from Proto-Indo-European ḱel- (“to cover”). c. 2
Etymology from Wiktionary, CC BY-SA