How would a native English speaker use ghastly and hideous? Is there any difference in context?
Ghastly: 1. Terrifyingly horrible to the senses : frightening. 2. intensely unpleasant, disagreeable, or objectionable.
Ghastly comes from a derivation of Old English gǣstan (“to torment, frighten”) with the suffix -lic. Equivalent to ghast/gast + -ly. Spelling with 'gh' developed 16th century from confusion with ghost; cf. also ghostly.
Hideous: 1. Frightful; shocking; extremely ugly. 2. Hateful, offensive.
From Middle English hidous, from Anglo-Norman hidous, from Old French hideus, hydus (“that which inspires terror”)
Ghastly, nowadays is generally used to convey a sense of ghostly fear or trepidation. (eg. Ghastly pale) while Hideous is generally used to convey unbearable ugliness or monstrosity (eg. hideous beast).
So loosely speaking, if you are dealing with something spooky, use ghastly, otherwise, use hideous to describe ugliness (like "It" from Stephen King's novel of the same name was hideous, not ghastly). Both are listed as synonyms in many dictionaries.