Sincere would be another word :)
The word serious, meaning "important" is an adjective.
Serious
A word that has the same meaning as another word is a synonym.
Another word meaning clenched is tighten.
The meaning of a word is its "definition."
serious
A synonym is a word with a meaning similar to that of another word.
Enraege
A seven-letter word meaning serious and eager could be "earnest".
earnest
Another word meaning "to influence" is "affect" or "impact."
Another word is I didn't do it! OR She/He did it.