"one who sets or puts in order," especially "one who tries to settle a quarrel," mid-15c., Scottish, agent noun from redd (v.).
Entries linking to redder
also red, c. 1300, redden, "to clear" (a space, etc.), "rid of encumbrance," from Old English hreddan "to save, free from (Satan, guilt, etc.), deliver, recover, rescue," from Proto-Germanic *hradjan (source also of Old Frisian hredda, Dutch redden, Old High German retten).
Sense evolution tended to merge it with unrelated rid. It is also possibly influenced by Old English rædan "to arrange," which is related to Old English geræde, source of ready (adj.). Related: Redding.
A dialect word in Scotland and northern England, where it has had senses of "to fix" (boundaries), "to comb" (out one's hair), "to separate" (combatants), "to settle" (a quarrel). The exception to the limited use is the meaning "to put in order, to make neat or trim" (1718), especially in redd up, which is in general use in England and the U.S. The same phrase, in the same sense, in Pennsylvania Dutch may be from cognate Low German and Dutch redden, obviously connected historically to the English word, "but the origin and relationship of the forms is not clear" [OED].