c. 1300, "an act of riding on horseback," especially in a festival procession, verbal noun from ride (v.). Meaning "teasing, annoying" is from 1927. As an adjective, "suitable for or associated with riding," Old English ridende. Riding-hood, originally a large hood worn by women when riding or exposed to weather, is from mid-15c., later a fashionable article of outdoor wear (18c.). Riding-boots, kind of high boots worn in riding, is from 1630s.
one of the three districts, anciently under the government of a a reeve, into which Yorkshire was divided, late 13c., from late Old English *þriðing, a relic of Viking rule, from Old Norse ðriðjungr "third part," from ðriði "third" (see third).
The initial consonant apparently was merged by misdivision with final consonant of preceding north, west, or east.