Etymology
From Middle English tan(c)kard(e), denoting 'a large tub for carrying liquid', perhaps related to Dutch tanckaert, from Middle Dutch tanckaert, meaning the same thing, but of uncertain ultimate origin. The OED suggests an alteration of Medieval Latin *kantard, from Latin cantharus (“tankard”). Klein suggests French tant quart (“as much of a quarter”).
Meaning "drinking vessel" is first recorded late 15th century.