Scrupulous means very careful to do things properly and correctly, such as paying friends back for money borrowed right away, or not returning a pair of shoes after they've been worn outdoors.
A scrupulous person is full of scruples, which are concerns about doing things that are morally right. Such a person is hesitant or doubtful, and might have trouble deciding what is morally right or wrong. The adjective scrupulous is from Latin scrūpulōsus, from scrūpulus "scruple." A near synonym is punctilious.