Alternatives: under-counter, under-the-counter
Located, belonging, or designed to be placed under the counter. Specifically: In communist countries, the so-called undercounter goods in shops were not offered to the public, but were hidden from customers by sellers who saved those items for their acquaintances, or sold them secretly in exchange for a bribe.
She answered the door with an undercounter scarcity Teflon-coated baking dish in her hand. (Context: The apartment was flooded by an overflown toilet; the parents are now hastily scooping water from the floor with kitchenware when the doorbell rings. Source: J∙ Okram - The Mystery of the Rammed Key.)