"deepest fear" is a correct and usable phrase in written English.
You can use it when you want to emphasize the intensity of someone's fear, for example: John overcame his deepest fear when he finally decided to go skydiving.
Our deepest fear is that we are powerful beyond measure.
My deepest fear: What if this is it?
On selection, the deepest fear of anti-academy campaigners, Gove has likewise played it both ways.
"Our deepest fear," the passage goes, "is not that we are inadequate.
France confronts its deepest fear again Saturday, when it plays Argentina in Montpellier.
It enacts the child's deepest fear of abandonment, weakness and vulnerability".
My deepest fear was that he would break the world record and then test positive for rum and Coke.
Still, Owen's deepest fear is being seen with another boy (Richard de Klerk) whose Hodgkin's has become leukemia.
When he arrived there on July 15, his deepest fear — deployment to Iraq or Afghanistan — seemed almost certain.
My deepest fear is not that the outrage economy remains alien but that we enter it wholeheartedly.
The collapse of the Soviet Union confirmed the Chinese Communist Party's deepest fear: that the end of party rule would mean the breakdown of order.
