under the counter Definition

counter¹
noun

1. A long flat-topped fitting in a shop, cafeteria, bank, etc over which goods are sold, food is served or business is transacted.
2. In various board games: a small flat disc used as a playing-piece, especially in board games.
3. A disc-shaped token used as a substitute coin.
4. A device for counting something.

Example: Geiger counter
5. Someone who counts.

Idiom: over the counter

By the normal method of sale in a shop, etc.

Idiom: under the counter

By secret illegal sale, or by unlawful means.

Etymology: 14c: from Latin computare to reckon.