The purpose of this research is to explore three English synonyms, namely critical, serious, and crucial, with a particular focus on meanings, degrees of formality, collocations, and semantic preferences. Two dictionaries, namely the Oxford Advanced Learner's Dictionary and the Cambridge Advanced Learner's Dictionary online, as well as the Corpus of Contemporary American English (COCA), were utilized as sources of information for the purpose of this research. It was shown that the two synonyms that are critical and crucial share the same core meaning and semantic preferences. However, the word serious is still distinct from the other two in terms of its particular meanings, degrees of formality, collocations, and semantic preferences. Because of this, the three words cannot be used interchangeably in any situation without causing confusion.