"horse, Indian pony of the northern Rockies," 1841, American English, said to be a Chinook (native Pacific Northwest) word; also the name of an Indian group and language (1825), of unknown origin.
"(self-)important person," 1912, short for Chinook jargon high muck-a-muck, literally "plenty of food" from muckamuck "food" (1847), which is of unknown origin. Also mucky-muck; muckety-muck.
1845, among some American native peoples, "a gift," from Chinook jargon pot-latch, "a gift," from Nootka (Wakashan) patshatl "giving, gift." Later (1865) in sense "An Indian feast, often lasting several days, given to the tribe by a member who aspires to the position of chief, and whose reputation is estimated by the number and value of the gifts distributed at the feast" [Century Dictionary, 1895]