n.
  - a feeling of doubt or hesitation with regard to the morality or propriety of an action.
 - historical a unit of weight equal to 20 grains used by apothecaries. 
▸archaic a very small amount.
 
v.
 hesitate or be reluctant to do something that one thinks may be wrong.
 
  Etymology
  ME: from Fr. scrupule or L. scrupulus, from scrupus, lit. ‘rough pebble’, (figuratively) ‘anxiety’.