"definitely vulnerable" is correct and usable in written English
You can use it to emphasize the idea that someone or something is very vulnerable, especially when you want to make a strong statement. For example: "The endangered species of kangaroos are definitely vulnerable and require urgent protection."
"We are definitely vulnerable," said Patrick D. O'Keefe, the city manager, who has proposed new taxes and cuts in spending and government hiring.
Cain and Bumgarner are both capable of dominating in a short series, but the team is definitely vulnerable after them, with Vogelsong being right around league-average and Lincecum not being a pitcher they can currently rely on.
Photograph: DOMINIQUE FAGET/AFP/Getty Images 4.11pm BST First set: Djokovic* 4-3 Raonic (*denotes server): Raonic may have a big forehand, but his backhand is definitely vulnerable and Djokovic is targeting it in the rallies to get some cheap points.
Florida's Jewish vote is definitely vulnerable to Republican appeals, but by 2016 the GOP's Jewish demographic window will have closed somewhat, nationally if not yet in Florida.
Skyscrapers are definitely more vulnerable to terrorism than low buildings.
"Men are definitely more vulnerable when they fly," says Robert Reiner, a Manhattan psychologist who treats people who are afraid of flying.
"He is taking positions that are out of the mainstream," she said, adding, "The types of votes he has taken definitely make him vulnerable".
According to the Unesco Atlas of the World's Languages in Danger, there are more than 100 languages in Russia that are vulnerable, definitely endangered, severely endangered or critical endangered.
So we definitely are most vulnerable and the front line of what is happening with climate change.
But building huge plants to harness it, often in remote, vulnerable areas, "definitely hurts the environment".
"We definitely need more people in vulnerable groups to be vaccinated, and if a public awareness campaign helps that, fine.
