Yours, Etc.: Origins and Uses of 8 Sign-Offs
early 13c., from Old French trubler (11c.), metathesis of turbler, from Vulgar Latin *turbulare, from Late Latin turbidare "to trouble, make turbid," from Latin turbidus (see turbid). Related: Troubled; troubling.
c.1200, "agitation of the mind, emotional turmoil," from Old French truble, related to trubler (see trouble (v.)). From early 15c. as "a concern, a cause for worry." The Troubles in reference to times of violence and unrest in Ireland is attested from 1880, in reference to the rebellion of 1640s.