See what I did there? Here are some common, yet often overlooked, examples of grammatical tautologies.
There are lots of tautological proper nouns, like the Los Angeles Angels (The the angels angels: Spanish) or Lake Tahoe (Lake the Lake: Washo). But they just are what they are.
Pleonasm can be syntactic or semantic.
Semantic pleonasm occurs when the grammar of a language allows for a word or words to be be left out of a sentence without changing the meaning. “That” is a commonly semantically pleonastic word in English:
“I thought that you had read it” can be replaced by “I thought you had read it.”
Syntactic pleonasm is what we more commonly call a redundancy, such as this one taken from a popular book:
What therefore God hath joined together, let no man put asunder.