A pleonasm is a literary device that uses a combination of words which adds unneeded complexity to the expression. A simple example is the phrase; "I saw it with my own two eyes" because the "own' is unnecessary, as the word "my" is already present. There is two types of pleonasm which are syntactic and semantic.
Syntactic Pleonasm Edit
A syntactic pleonasm is a word that is optional in its function in the sentence. A common example is the sentence, "I know that you are coming" because the word 'that' can be removed without making the sentence ungrammatical.
Semantic Pleonasm Edit
Semantic pleonasms are words or phrases that are useless in the context of the sentence and can be down without. One well known example would be the sentence "the plumber fixed our hot water heater" because a heater is obviously making hot water, and the word "hot" is not needed to convey the message. Another example is the phrase "actual fact" instead of "fact" because a fact is factual, and there is no need to provide the word "actual."