from Wiktionary, Creative Commons Attribution/Share-Alike License
- adv. Illicitly, against regulations, of goods kept under the serving counter in a shop to be unobtrusively passed to a customer who knows they are available for surreptitious sale (e.g. pornographic magazines in a newsagent).
- adj. (Particularly with regard to payment or tax avoidance) In an underhand way, sneakily. Unofficially.
under + the + (retail sales) counter (Wiktionary)