Flank

1. The flesh between the last rib and the hip; the side. The meat from that location. The flank is not a top cut of meat.
2. (nautical) Maximum speed a vessel can sustain without excessive engine wear or risk of damage. Typically used in an emergency or during an attack.
3. The extreme left of right edge of a military formation, army etc. They enemy attacked our right flank.
4. To attack the flank(s) of something. It was a flank attack. They tried to flank us.