In a frowsy manner; in a musty, stuffy, or slovenly way.
From 'frowsy' (or 'frowzy') plus the adverbial suffix '-ly', which transforms adjectives into adverbs describing how something is done or how someone appears.
Adverbs like 'frowsily' are somewhat rare in everyday speech, but they're crucial for detailed description—they let a writer show us not just what something is, but exactly how it presents itself to the senses.
Complete word intelligence in one call. Free tier — 50 lookups/day.