ghastly

The word 'ghastly' originates from the Middle English verb 'gasten', meaning "to terrify or frighten," which itself comes from the Old English 'gǣstan', a derivative of 'gāst', meaning "spirit or ghost." The core semantic thread is the terror inspired by an encounter with a spectral being. Over time, the adjectival form 'gastlich' (terrifying) solidified, and its spelling was altered in the 16th century under the influence of 'ghost' to become 'ghastly'. This evolution transformed a word describing an action ("to terrify") into one describing a quality—something so horrifying it evokes the pallor and dread of seeing a ghost.

The word is a simplex form derived from the Middle English 'gastlich', from 'gasten' (to terrify) + the adverbial suffix '-ly', which later became an adjective-forming suffix. The initial 'gh-' spelling was influenced by the unrelated word 'ghost'.