If you describe someone as an ingrate, you are criticizing them because they do not express thanks to someone who has helped them—they are ungrateful.
If people try to ingratiate themselves with you, they try to get your approval by doing or saying things that they think will please you.
If something is gratuitous, it is freely given; nevertheless, it is usually unnecessary and can be harmful or upsetting.
When you have a feeling of gratification, you experience satisfaction or pleasure about a job well done.
When you congratulate someone, you say that they did a great job on something or wish them well about something that happened to them.
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