The phrase "a very assiduous" is correct and usable in written English.
It can be used to describe someone who is very diligent or hardworking in their efforts.
Example: "She is a very assiduous student, always putting in extra hours to understand the material."
Alternatives: "a very diligent" or "a very industrious".
Rumour suggests that he has not been a very assiduous student.
He has a fascination with newspapers – he is probably better than anyone in Tory circles at knowing how to pitch a story – and he is a very assiduous student of other parties".
"It was a terrific victory for Douglas Carswell, he's obviously been a very assiduous MP, he's very popular," Mr Davies, MP for Montgomeryshire," told BBC Radio Wales.
He was a very assiduous and diligent student, and became a lawyer.
"One man was very assiduous in attending the mosque in Madrid," the official said.
"I think the Federal Reserve does have the capacity, the tools, should deflation occur — which, again, I don't believe is very likely — to reverse it, and we would be very assiduous in doing that," the chairman added.
"The Victorians were very assiduous about collecting information; and while some of the landings might have been missed from smaller ports, the larger ports were covered very efficiently," he told BBC News.
All week Bill Parcells had been telling his Dallas Cowboys that the difference between a very good team and an also-ran was assiduous attention to detail.
He owed his unexpected victory to one masterful, notes-free speech broadcast live to the nation, not an assiduous campaign to slowly win over Lobby scribblers.Despite his social ties with Rebekah Brooks, Mr Cameron has never actually been a very keen schmoozer of newspaper journalists.
What he was though was an effective, assiduous and very hard-working man.
Since Adam is a highly assiduous follower of my work, he should know that I take very seriously disciplines such as history, and philosophy, and theology, and literature, as explanations of the world, even though they are not sciences.
