Tautology is expressing an idea, statement, or word that says the same thing twice, just in a different way. We often use tautologies without even thinking!
Example: They hiked to the summit at the top of the mountain.
In this sentence summit and top are tautological because they have similar meanings, so there is no need to use both words. The sentence could be written as:
They hiked to the summit.
They hiked to the top of the mountain.
Some common tautologies are: