Definition of flank:
(adj) :
nautical: Maximum (of speed). Historically faster than full speed (the most a vessel can sustain without excessive engine wear or risk of damage), now frequently used interchangeably. Typically used in an emergency or during an attack (All ahead flank!)
(n) :
the flesh between the last rib and the hip; the side; a cut of meat from the flank of an animal
(v) :
to attack the flank(s) of something; to defend the flank(s) of something