Using Corpus of Contemporary American English as the source data, this paper carries out a corpus-based behavioral profile study to investigate four near-synonymous adjectives (serious, severe, grave, and grievous), focusing on their register and the types of nouns they each modify. Although sharing core meaning, these adjectives exhibit variations in formality levels and usage patterns. The identification of fine-grained usage differences complements the current inadequacies in describing these adjectives. Furthermore, the study reaffirms the effectiveness of the corpus-based behavioral profile approach in examining synonym differences.