No, it's not safe in that scenario. "Destructive" means throwing away anything, even one word the user typed. Do not use the word "cancel" for that operation - use the word "Discard" or an X button, with an are-you-sure prompt that has a cancel button that safely brings you back to the editing interface.
Edit: OK, maybe "one word" is an exaggeration. Certainly for the case of a form of input fields a no-prompt cancel button is inappropriate. However, if you have a simple OK/Cancel dialogue that contains a single one-line input field, it is usually acceptable to have a Cancel button that throws away your input without prompting.
If I'm filling out a modal form and "Cancel" doesn't result in a clean form after I open it again, it should probably say something like "Hide" or "Finish later" instead.
No, it's not safe in that scenario. "Destructive" means throwing away anything, even one word the user typed. Do not use the word "cancel" for that operation - use the word "Discard" or an X button, with an are-you-sure prompt that has a cancel button that safely brings you back to the editing interface.
Edit: OK, maybe "one word" is an exaggeration. Certainly for the case of a form of input fields a no-prompt cancel button is inappropriate. However, if you have a simple OK/Cancel dialogue that contains a single one-line input field, it is usually acceptable to have a Cancel button that throws away your input without prompting.