"wet, soft, spongy ground with soil chiefly composed of decaying vegetable matter," c. 1500, from Gaelic and Irish bogach "bog," from adjective bog "soft, moist," from Proto-Celtic *buggo- "flexible," from PIE root *bheug- "to bend." Bog-trotter applied to the wild Irish from 1670s.
A bog is characterized by vegetation, decayed and decaying, and a treacherous softness. A quagmire or quag is the worst kind of bog or slough; it has depths of mud, and perhaps a shaking surface. A slough is a place of deep mud and perhaps water, but generally no vegetation. [Century Dictionary]
Procopius' 6c. Anecdota, unpublished memoirs of Emperor Justinian full of court gossip, gave the word a sense of "revelation of secrets," which decayed in English to "brief, amusing story" (1761).
late 15c., "to decrease," also "to decline, deteriorate, lose strength or excellence," from Anglo-French decair, Old North French decair (Old French decheoir, 12c., Modern French déchoir) "to fall, set (of the sun), weaken, decline, decay," from Vulgar Latin *decadere "to fall off," from de "off" (see de-) + Latin cadere "to fall" (from PIE root *kad- "to fall").
Transitive sense of "cause to deteriorate, cause to become unsound or impaired" is from 1530s. Sense of "decompose, rot" is from 1570s. Related: Decayed; decaying.
"famous deed, exploit," more commonly "story of great deeds, tale of adventure," c. 1300, from Old French geste, jeste "action, exploit, romance, history" (of celebrated people or actions), from Medieval Latin gesta "actions, exploits, deeds, achievements," noun use of neuter plural of Latin gestus, past participle of gerere "to carry on, wage, perform," which de Vaan says is considered to be from the same root as agere "to set in motion, drive forward, do, perform" (from PIE root *ag- "to drive, draw out or forth, move"). Now only as a deliberate archaism. Jest (n.) is the same word, with a decayed sense.
c. 1500, "old or decayed tree stump" (Douglas), a provincial word of unknown origin. The meaning was extended to "small ox or cow," especially of the breeds characteristic of Wales and the Scottish Highlands (1540s, if indeed this is the same word), and by 1610s generally to undersized animals and ignorant people.
The slang sense of "person of low but thick-set build; a stocky, stunted person," a term of abuse, is by 1700. The sense of "smallest of a litter" (especially of pigs) is attested from 1841 as a Shropshire word, though it seems to have become general in American English. Some see a connection of runt, at least in the "animal" sense, to Middle Dutch runt "ox," but OED thinks this unlikely, and pronounces the word "of obscure origin." Related: Runty (1807); runtish (1640s).