Extremely dry, either from heat or lack of water, or desperately thirsty.
From Middle English 'perchen' or 'parch,' possibly from Old French or Latin 'perdicare.' The exact origin is uncertain but may relate to making something thoroughly dry.
Deserts and plants use the word 'parched' the same way—it describes that point of desiccation where something is so dry it's starting to crack and wither, whether that's soil or your lips.
Complete word intelligence in one call. Free tier — 50 lookups/day.