Insensitivity to criticism or insult, as in You can tell him exactly what you think of his new piece; unlike most composers he has a thick skin. This term transfers an impervious outer coating to mental or emotional toughness. [Mid-1500s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.