Definition of as fit as a flea in English:

as fit as a flea

phrase

(also fit as a flea)
British
  • In very good health.

    muscular, muscly, sturdy, strapping, well built, powerfully built, strong, powerful, robust, able-bodied, vigorous, hardy, lusty, hearty, hale and hearty, brawny, burly, broad-shouldered, thickset, Herculean