(To) be on tenterhookks is a phrase. It is used for a situation when someone is in a state of very painful anxiety or suspense.
1. Sameera was on tenterhooks when she noticed that her colleagues in the office were plotting against her.
2. We were on tenterhooks when we saw that the old beggar was lying unconscious on the roadside.
3. When he discovered that his son had left home empty-handed, he was on tenterhooks.