nod off

nod off idiom
Fall asleep momentarily, doze, as in Grandma spends a lot of time in her rocking chair, nodding off now and then. This expression alludes to the quick involuntary dropping of one's head from an upright position when drowsy or napping. The verb nod alone was so used from the mid-1500s. Also see drop off, def. 1.

The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

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