E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Wearing the leek on St. Davids day. Mr. Brady says St. David caused the Britons under King Cadwallader to distinguish themselves by a leek in their caps. They conquered the Saxons, and recall their victory by adopting the leek on every anniversary (March 1st). (Clavis Calendaria.) Wearing the leek is obsolete. (Anglo-Saxon lec.)
Shakespeare makes out that the Welsh wore leeks at the battle of Poitiers, for Fluellen says:
If your majesties is remembered of it, the Welshmen did good service in a garden where leeks did grow, wearing leeks in their Monmouth caps, which, your majesty know, to this hour is an honourable badge of the service; and I do believe your majesty takes no scorn to wear the leek upon St. Tavys Day.Henry V., iv. 7.
To eat the leek. To be compelled to eat your own words, or retract what you have said. Fluellen (in Shakespeares Henry V.) is taunted by Pistol for wearing a leek in his hat. Hence, says Pistol, I am qualmish at the smell of leek. Fluellen replies, I peseech you . . at my desire . . to eat this leek. The ancient answers, Not for Cadwallader and all his goats. Then the peppery Welshman beats him, nor desists till Pistol has swallowed the entire abhorrence.