Use 'bluesy' to describe a distinct genre of music with roots in the African-American history. He added a harmonica for that bluesy sound.
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Emotional Mood
'Bluesy' can imply a sad or soulful mood, like the musical form it originates from. Her voice has such a bluesy melancholy to it.
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Cultural Emphasis
'Bluesy' often evokes the Southern United States and the early 20th-century atmosphere. His lyrics are so bluesy, like they're straight out of Memphis.