subs. (colloquial).The furcula or forked bone of a fowls breast.
1598. FLORIO, A Worlde of Wordes, s.v. Catriosso, the bone called the MERIE THOUGHT.
1694. ECHARD, Plautus [Encyclopædic Dictionary]. Let him not be breaking MERRY-THOUGHTS under the table with my cousin.
1711. ADDISON, The Spectator, No. 7, 8 March. I have seen a man in love grow pale, and lose his appetite, upon the plucking of a MERRY-THOUGHT.