Nabab (נָבַב) means to make hollow — to bore out, excavate, or create a cavity. From this root comes nub (fruit, product) in some analyses, though more directly it produces neqeb (cavern). The concept of hollowness carries both practical and metaphorical weight.
Hollowness in Scripture is ambiguous: the hollow of God's hand shelters Elijah (1 Kings 19:13 — a cave); the hollow altar of the Tabernacle (Exod. 27:8) is made of acacia wood, hollow, portable, fit for a journey. Yet hollow weights and measures are deception (Prov. 11:1). And the hollow self — empty of God — is the condition of the fool (Psalm 14:1, nabal — the "hollow" or empty one). To be filled is the spiritual aspiration: "Be filled with the Spirit" (Eph. 5:18) — the antidote to the spiritual nabab.
The theological value of nabab lies in the images it generates: the hollow altar (portable, servant-shaped), the hollow of God's hand (vast yet personal). The opposite of hollow is male (H4390, to be full) — and the Psalmist's longing is for God to fill what is empty. The hollow vessel is useless until filled; the hollow person is incomplete until inhabited by the divine Spirit.