(combat sports) blow below the belt, low blow, groin attack (unfair or illegal blow that lands below the opponent’s waist) / (figuratively) low blow, cheap shot (any attack that is considered unfair or unscrupulous)

(dated, derogatory) bluestocking

(dated) shallow area of the sea

(historical) Lower Canada

hats off

plural of bas-fond

down here, here below / yonder

(archaic) the taking down of hammocks in a ship / (idiomatic) commotion; hoo-ha

Bas-Rhin (a department of Grand Est, France)

(nautical) lower-mast (when it is multiple sections)