¹leech

parasite, sycophant, toady, leech, sponge mean a usually obsequious flatterer or self-seeker. parasite applies to one who clings to a person of wealth, power, or influence or is useless to society <a jet-setter with an entourage of parasites>. sycophant adds to this a strong suggestion of fawning, flattery, or adulation <a powerful prince surrounded by sycophants>. toady emphasizes the servility and snobbery of the self-seeker <cultivated leaders of society and became their toady>. leech stresses persistence in clinging to or bleeding another for one's own advantage <a leech living off his family and friends>. sponge stresses the parasitic laziness, dependence, and opportunism of the cadger <a shiftless sponge, always looking for a handout>.

Originally the English word leech meant “doctor.” Centuries ago doctors thought that a good way to cure sick people was to make them bleed. The blood of a sick person supposedly had harmful things in it that would flow away with the blood. To take bad blood out of sick people, early doctors often used little worms that suck blood. Leech, the word for a doctor, came to be used for these worms as well.