Meaning

• An avoirdupois ounce, weighing 1/16 of an avoirdupois pound, or 28.3495 grams.

• A troy ounce, weighing 1/12 of a troy pound, or 480 grains, or 31.1035 grams.

• A US fluid ounce, with a volume of 1/16 of a US pint, 1.8047 cubic inches or 29.5735 millilitres.

• A British imperial fluid ounce, with a volume of 1/20 of an imperial pint, 1.7339 cubic inches or 28.4131 millilitres.

• A little bit.

  "He didn't feel even an ounce of regret for his actions."