stem-winder

Etymology
US, mid-late 19th century, originally referring to then-recent stem-wind watches (invented in 1840s, commercialized initially 1850s by ). These were expensive, top-notch watches, hence generalized (1892 ) to “top-notch”, particularly applied to speeches, or to the orator in question. Non-speech senses later fell out of use. Nuance of “rousing” speech possibly by analogy with watch being.

Circa 2000, later sense of “interminable speech” a folk etymology, in sense “a speech that lasts so long one must wind one’s watch”.

Noun

 * 1) A watch that is wound up by turning a small knob (at the stem).
 * 2)  A rousing speech, especially by a politician.
 * 3)  Someone who gives such speeches; a great orator.
 * 4)  A boring, interminable speech.
 * 5) * 2000, Bill Schneider and Keating Holland, “What to look for Thursday at the Democratic National Convention”, August 17, 2000, , “Clinton comparisons”:
 * Or – heaven forbid – the of 1988, who gave a tedious stemwinder in 1988 that has gone down in the books as the worst nominating speech in recent memory?
 * 1)  Something top-notch or first-rate.

Usage notes
Note contradictory senses of “rousing speech” (earlier sense) and “boring speech” (later sense); use in the latter sense may be proscribed as a corruption, and is a folk etymology.