What does thorough mean?
Thorough describes something complete, detailed, and carefully attended to. A thorough investigation examines every relevant aspect, while a thorough understanding means grasping a subject in depth rather than merely knowing its broad outline. The word commonly suggests both scope and care: an examination is thorough because it is extensive, but also because little is overlooked. It is useful in contexts where quality and completeness matter, such as research, review, preparation, and analysis. Although thoroughly can modify the verb “do” or “clean,” its basic force remains the same: the action is carried out to the full extent and with close attention to detail. The related adverb thoroughly and noun thoroughness allow the same idea to be expressed as a manner or quality. The word is established in both British and American English and is not restricted to a particular professional field.
Complete in every detail; careful and exhaustive.
"The doctor gave the patient a thorough explanation of the treatment."
The sense may range from broadly comprehensive to painstakingly meticulous, depending on context.
A thoroughbred horse.
"The young thorough won her first race by several lengths."
This noun use is much less common than the adjective and is chiefly associated with horse racing and stud farming.
Plural forms are used for thoroughbred horses considered individually.
"The owner purchased several thoroughs at the autumn sale."
Thorough began as a form of “through,” so its sense of doing something all the way from beginning to end grew out of the idea of passing through.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does thorough come from?
The word comes from Middle English thurgh, an earlier form of through, which descended from Old English þurh. Its sense of being complete or going through something from beginning to end developed through the idea of passing through without skipping any part. It is closely related to through and belongs to a family that includes throughout, thoroughfare, and thoroughbred.
Related word forms
How thorough is actually used
The word is neutral to formal in most contexts but often suggests painstaking care and attention to detail. It can be approving when praising someone's work, while “too thorough” may imply unnecessary or excessive detail.
Easily confused with thorough
A thorough person or process is complete and careful, whereas something done through something passes from one side or stage to another.