Heck (interjection)

1. Used to express mild surprise, dismay, or dissatisfaction.
2. Used as a mild or polite substitute for stronger expletives.
3. Used as a mild or polite substitute for "hell".

Origin:

Shortened form of "what the heck" or "hell".

Examples:

1. Heck, I forgot my keys.
2. Heck, I don't know how to fix this.
3. Heck, I wish I could come but I have other plans.
4. Heck, I'm not sure what to do.
5. Heck, I didn't expect that.