a Unitarian preacher and son of Peter (4), was born in Boston, Mass., in 1785. He graduated at Harvard College in 1804, and immediately after his graduation commenced his theological studies under the direction of Rev. William E. Channing. In the early part of 1805 Mr. Thacher took charge of the Boston Latin Grammar-school, but in the summer of 1806 was chosen to be the traveling companion of Rev. Mr. Buckminster. Returning in September, 1807, he was shortly after appointed librarian of Harvard College, and entered on his duties in 1808. He prosecuted his theological studies at Cambridge, and succeeded Dr. Kirkland as pastor of the New- South Church, May 15, 1811, retaining this connection until his death, at Moulins, France, Jan. 2, 1818. His principal publications were, Apology for Rational and Evangelical Christianity, a discourse (Bost. 1815, 8vo): — Unity of God, a sermon (Liverpool, 1816, 8vo; 2d Amer. ed. Worcester, 1817, 8vo): — Sermons, with a Memoir by Rev. F. W. P. Greenwood (Bost. 1824, 8vo): — Evidence Necessary to Establish the Doctrine of the Trinity (1828, 12mo). See Allibone, Dict. of Brit. and Amer. Authors, s.v.; Sprague, Annals of the Amer. Pulpit, 8:435 sq.