scruple

Concise Oxford English Dictionary © 2008 Oxford University Press:
scruple/ˈskruːpl/

▶noun

• 1 a feeling of doubt or hesitation with regard to the morality or propriety of an action.

• 2 historical a unit of weight equal to 20 grains used by apothecaries.

  ■ archaic a very small amount.

▶verb hesitate or be reluctant to do something that one thinks may be wrong.

– origin ME: from Fr. scrupule or L. scrupulus, from scrupus, lit. ‘rough pebble’, (figuratively) ‘anxiety’.