harangue; fervent speech; grand oration
Refers to a passionate, often lengthy public speech, sometimes with a connotation of being overblown or theatrical.
彼は広場で大演説をぶった。
He delivered a fervent speech in the square.
選挙前の大演説会には多くの人が集まった。
Many people gathered for the grand speech rally before the election.
Compound of 大 (dai, 'big, great') and 演説 (enzetsu, 'speech, address'). The exact historical derivation is uncertain, but the word is transparently formed from these elements.