Superlative form of lengthy: most lengthy.(adjective)
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Use "lengthiest" in a sentence
"The lengthiest diatribe comes in the current US issue of GQ magazine, where film writer Mark Harris rails against the branding of Hollywood studio movies, a trend that prizes brand recognition and marketing over originality."
"Ruskin's final, and lengthiest, point is not about any physical attribute -- it is rather a critical analysis of the role of the horse in fostering social inequality."
"As the economy experienced one of the largest and lengthiest economic booms in history from 1982-2007, the left moaned that the gains went to yacht club members."