clear as crystal

(as) clear as crystal

Easily visible or understandable. I want the language in these legal contracts to be as clear as crystal so that there is no confusion. The sign is right there on the door—it's as clear as crystal.
See also: clear, crystal
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

*clear as crystal

 
1. Cliché very clear; transparent. (*Also: as ~.) The stream was as clear as crystal. She cleaned the windowpane until it was clear as crystal.
2. Cliché very clear; easy to understand. (*Also: as ~.) The explanation was as clear as crystal. Her lecture was not clear as crystal, but at least it was not dull.
See also: clear, crystal
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.

clear as crystal

1. If something is as clear as crystal, it is transparent or very clear. It was a brilliant blue day, as clear as crystal, with a sun that was just comfortably hot. Note: People also use the more frequent adjective crystal clear. The water is crystal clear.
2. If something is as clear as crystal, it is very obvious or easy to understand. The policy is very clear - it's as clear as crystal. Note: People also use the more frequent adjective crystal clear. Make sure your instructions are crystal clear.
See also: clear, crystal
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012
See also:
References in classic literature ?
Around the edge of the pool were set rows of fine emeralds as large as door-knobs, while the water of the bath was clear as crystal.