Capable of being furnished, equipped, or outfitted with furniture, supplies, or necessary items.
From furnish (Old French fournir meaning 'to provide') + -able (Latin -abilis indicating capability), meaning 'able to be furnished or outfitted.'
The suffix -able is one of English's superpowers—once you understand it, you can guess the meaning of hundreds of words you've never seen before, and furnishable is a perfect example of how productive this pattern is.
Complete word intelligence in one call. Free tier — 50 lookups/day.