Gratuitous and grateful look similar, but they mean very different things.
Gratuitous usually describes something unnecessary, excessive, or unwarranted. It can also mean given freely, but in modern everyday use it often has a negative tone. If someone makes a rude comment for no good reason, you might call it a gratuitous insult.
Grateful means thankful or appreciative. It describes a feeling, not an extra action or detail. If someone helps you during a difficult week, you might say, I am grateful for your support.
- Use gratuitous for something extra that was not needed: The movie included gratuitous violence.
- Use grateful for a feeling of thanks: She felt grateful for the second chance.
A quick memory tip helps: grateful is about gratitude. Gratuitous is about something added, often when it should not have been.