Definition of rely on/upon
1 : to need (someone or something) for support, help, etc. : to depend on (someone or something) My mother relied on me for financial support. They rely on a well for all their water.
2 : to trust or believe (someone or something) She's someone you can rely on. I relied heavily upon your advice. You could always rely on him to disagree.
3 : to expect (something) with confidence : to be certain that (something) will happen or exist The economy may improve next year, but it's not something you can rely on.
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