a good Samaritan
US /ə ɡʊd səˈmær.ɪ.tən/
UK /ə ɡʊd səˈmær.ɪ.tən/
1.
a person who helps other people, especially strangers, in a difficult situation
:
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A good Samaritan stopped to help the stranded motorist change a flat tire.
•
The old woman thanked the good Samaritan who returned her lost wallet.