Definition of water chickweed in US English:

water chickweed

noun

  • (Originally) any of various small, often straggling or decumbent herbaceous plants of wet or damp habitats; (in later use) specifically Myosoton aquaticum (family Caryophyllaceae), a white-flowered perennial of temperate Eurasia.

Origin

Mid 17th century; earliest use found in Thomas Johnson (d. 1644), apothecary and soldier.