cowardice
A lack of courage to do what is right or needed.
Cowardice is the quality of lacking courage when courage is needed, especially when there's something important at stake. A person showing cowardice runs away from difficulty or danger when they should stand firm, or stays silent when they should speak up.
Cowardice isn't the same as fear. Everyone feels fear when facing something scary or difficult. The difference is what you do with that fear. A student who copies homework because they're afraid of getting a bad grade shows cowardice. A teammate who watches a friend get blamed for something they didn't do, but stays quiet to avoid trouble, acts with cowardice.
The word often appears in discussions of moral choices. When people face a moment where doing the right thing requires bravery, choosing the easy path instead is cowardice. A coward is someone who habitually avoids difficulty or danger in this way.
Cowardice can have lasting effects. Abandoning your responsibilities when others are counting on you can be hard to forgive or forget.