a thorough combing or brushing of the hair.

Origin of comb-out

First recorded in 1915–20; noun use of verb phrase comb out Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for comb out

comb out

verb (tr, adverb)

to remove (tangles or knots) from (the hair) with a comb
to isolate and remove for a purpose
to survey carefully; examine systematically

noun comb-out

an act of combing out
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012