Idioms and Phrases with lost in thought
lost in thought
Concentrating on or pondering over something. For example, Gwen didn't hear a word you said; she was lost in thought.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.