"thoroughly" is correct and usable in written English
You can use it as an adverb to mean "in a very careful and detailed manner". For example: "I thoroughly examined the evidence before making my decision."
M Zola remarked that it surprised him that no novelist had depicted the great city thoroughly.
You say that you respect Parliament, that you answered more questions than your predecessors and that you are the first Prime Minister to appear before a select committee, but in other ways you seem thoroughly hostile to the idea of scrutiny by elected representatives.
Sounds like a 1970s porno, but is actually an ancient and thoroughly respectable Arabic pastime, and the second it started, it immediately went to the top of my "Why El Fenn is better than everywhere else" list.
These rapes (some allegedly involving underaged individuals) are not thoroughly reported on, as the department of immigration is not keeping formal records.
While Honor Blackman thoroughly enjoys herself at the OM fashion shoot and likes the clothes - the Alexander McQueen shirt, Miu Miu trousers and Banana Republic Oxford bags draw particular praise - she hates shopping for outfits herself.
There are 180 official 'sex businesses' in the De Wallen quarter, the Amsterdam red light district, which employ about 2,000 prostitutes who are registered, thoroughly inspected and pay tax.
Charles Kennedy (Former leader of Liberal Democrats dies aged 55, theguardian.com, 2 June) was a rarity in public life: a thoroughly decent man who was honest enough to admit his failings and who was not treated kindly for doing so.
Mendes's award for direction is the most thoroughly and conspicuously deserved of the list.
The bad news for the people of the world is we were lied to thoroughly by everybody for nearly 20 years.
Upstairs, the barman would thoroughly prepare a pisco sour, the national drink, at any time of day.
The cabins were comfortable and unpretentious, but serviced as thoroughly as any hotel.
