This adjective describes something that cannot be approached or accessed—whether an inaccessible mountain, an unapproachable person, or in theological terms, the transcendent glory of God that no human can draw near to. Classical usage includes geographical barriers (impassable mountains) and social barriers (persons too exalted or guarded to approach). Paul employs it to describe God's dwelling in 'unapproachable light,' emphasizing the infinite gulf between human creatureliness and divine majesty.