coward
A person who lets fear stop them from doing right.
A coward is someone who lacks courage when facing danger, difficulty, or fear. When soldiers abandon their posts in battle, when a bully picks on smaller kids but runs from anyone their own size, or when someone lets their friends take the blame for something they all did together, that's cowardly behavior.
Everyone feels afraid sometimes: that's normal and healthy. A coward lets fear control their choices, especially when doing the right thing requires bravery. The opposite of a coward isn't someone who never feels fear, but someone who acts with integrity despite being afraid.
Cowardice is the noun that describes cowardly behavior. Throughout history, societies have viewed cowardice as shameful because communities depend on people who won't abandon each other when things get hard.