also logjam, "congestion of logs on a river," by 1851, American English; see log (n.1) + jam (n.2). The figurative sense is by 1890.
Entries linking to log-jam
log n.1
unshaped large piece of tree, early 14c., of unknown origin. Old Norse had lag "felled tree" (from stem of liggja "to lie," hence "a tree that lies prostrate"), but many etymologists deny on phonological grounds that this can be the root of English log. Instead, they suggest an independent formation meant to "express the notion of something massive by a word of appropriate sound" [OED, which compares clog (n.) in its original Middle English sense "lump of wood"].
Log cabin (1770) was the typical dwelling of the poor in antebellum U.S. history in the well-timbered region that was then the West. It has been a figure of the honest pioneer since the 1840 presidential campaign of William Henry Harrison (the original application was derisive and either way it was inaccurate). Falling off a log as a type of something easy to do is from 1839.
jam n.2
"a tight pressing between two surfaces," 1806, from jam (v.). Sense of "machine blockage" is from 1890, which probably led to the colloquial meaning "predicament, tight spot," first recorded 1914. Jazz meaning "short, free improvised passage performed by the whole band" dates from 1929, and yielded jam session (1933); but this is perhaps from jam (n.1) in sense of "something sweet, something excellent."