"Let's mosey on down t' the Agora for a spell, pardner!"
But the Online Etymology Dictionary suggests this origin:The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
mosey
SYLLABICATION: mo·sey
PRONUNCIATION: mō'zē
INTRANSITIVE VERB: Inflected forms: mo·seyed, mo·sey·ing, mo·seys
Informal 1. To move in a leisurely, relaxed way; saunter: moseyed over to the club after lunch. 2. To get going; move along.
ETYMOLOGY: Origin unknown.
The American Heritage® Dictionary of the English Language, Fourth Edition. Copyright © 2000 by Houghton Mifflin Company. Published by the Houghton Mifflin Company. All rights reserved.
mosey
1829, Amer.Eng. slang, of unknown origin, perhaps related to British dial. mose about "go around in a dull, stupid way." Or perhaps from Sp. vamos (see vamoose).