What is the fallacy when you use a word with different meanings as if to mean the other?

For example: Christians will say atheism is a religion because one definition of religion is "a pursuit or interest to which someone ascribes supreme importance. 'consumerism is the new religion'" but this is NOT the use of the word when talking about religion with religious people. When talking... show more For example: Christians will say atheism is a religion because one definition of religion is "a pursuit or interest to which someone ascribes supreme importance.
'consumerism is the new religion'" but this is NOT the use of the word when talking about religion with religious people.

When talking about religion, the context is this definition, "the belief in and worship of a superhuman controlling power, especially a personal God or gods."

So what is the fallacy when people try to manipulate the use of a word?
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