slang Utterly crazy or insane. ("Loco" means "mad" or "crazy" in Spanish, with "plumb" being used as an intensifier.) Primarily heard in US. This idea of yours is plumb loco. Poor guy went plumb loco after his wife died.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
Rur. completely crazy. (Loco is from a Spanish word meaning "mad.") You're plumb loco if you think I'll go along with that. All those people were running around like they were plumb loco.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
plumb loco(ˈpləm ˈloko)
mod. completely crazy. (Folksy. Loco is from a Spanish word meaning “mad.”) You’re plumb loco if you think I’ll go along with that.
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.