What is "penny grass"

Penny \Pen*ny\, n.; pl. Penniesor Pence. Pennies denotes the number of coins; pence the amount of pennies in value. [OE. peni, AS. penig, pening, pending; akin to D. penning, OHG. pfenning, pfenting, G. pfennig, Icel. penningr; of uncertain origin.]

1. An English coin, formerly of copper, now of bronze, the twelfth part of an English shilling in account value, and equal to four farthings, or about two cents; -- usually indicated by the abbreviation d. (the initial of denarius).

   Note: ``The chief Anglo-Saxon coin, and for a long period the only one, corresponded to the denarius of the Continent . . . [and was] called penny, denarius, or denier.''
   --R. S. Poole. The ancient silver penny was worth about three pence sterling (see Pennyweight). The old Scotch penny was only one twelfth the value of the English coin. In the United States the word penny is popularly used for cent.

2. Any small sum or coin; a groat; a stiver.
   --Shak.

3. Money, in general; as, to turn an honest penny.

   What penny hath Rome borne, What men provided, what munition sent?
   --Shak.

4. (Script.) See Denarius.

   Penny cress (Bot.), an annual herb of the Mustard family, having round, flat pods like silver pennies ( Thlaspi arvense).
   --Dr. Prior.

   Penny dog (Zo["o]l.), a kind of shark found on the South coast of Britain: the tope.

   Penny father, a penurious person; a niggard. [Obs.]
   --Robinson (More's Utopia).

   Penny grass (Bot.), pennyroyal. [R.]

   Penny post, a post carrying a letter for a penny; also, a mail carrier.

   Penny wise, wise or prudent only in small matters; saving small sums while losing larger; -- used chiefly in the phrase, penny wise and pound foolish.

n. foetid Eurasian weed having round flat pods; naturalized throughout North America [syn: field pennycress, French weed, fanweed, stinkweed, mithridate mustard, Thlaspi arvense]