/ ˈθʌrə; NAmE ˈθɜːroʊ/ adjective
1.
done completely; with great attention to detail :
a thorough knowledge of the subject
The police carried out a thorough investigation.
2.
[ not usually before noun ] ( of a person ) doing things very carefully and with great attention to detail :
She's very thorough and conscientious.
3.
( BrE , informal ) used to emphasize how bad or annoying sb/sth is
SYN complete :
Everything was in a thorough mess.
► thor·ough·ness noun [ U ]:
I was impressed by the thoroughness of the report.
I admire his thoroughness.
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WORD ORIGIN
Old English thuruh , alteration of thurh through . Original use was as an adverb and preposition, in senses of through . The adjective dates from the late 15th cent., when it also had the sense that goes or extends through something , surviving in thoroughfare .