Synonyms are 2 or more Words which mean the same thing, or at least mean something very similar. For instance, scream and screech mean about the same thing but are different words.
More specifically, you can say that two word forms a synonym when they share (almost) the same word sense.
Formal definition of the book page 104 More formally, two words are synonymous if they are substitutable for one another in any sentence without changing the truth conditions of the sentence, the situations in which the sentence would be true. We often say in this case that the two words have the same propositional meaning.
Definition in the lecture Synonyms are words which can be substituted with each other in some context. Hence, two words are more similar when the overlap of their contexts is large.
Often the meaning is not exactly the same. You can use this website to find synonyms. Words can also be similar in other ways, see word similarity.
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