Cursed, damned, or under a curse; wickedly evil or deserving of misfortune.
Either from accourse (obsolete past tense of accurse) or a poetic/archaic variant of accursed, both ultimately from Latin accursus. The -t ending is characteristic of old English past participles.
Poets absolutely adored 'accurst' because it's shorter than 'accursed' but sounds even MORE archaic and dramatic—you can almost hear the Middle Ages in it!
Complete word intelligence in one call. Free tier — 50 lookups/day.