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
Another word meaning "to influence" is "affect" or "impact."
The word that means overly serious or lacking in humor is "sombre" (or "somber" in American English). It describes a demeanor or attitude that is grave, serious, or dismal, often devoid of lightness or levity. Another term that conveys a similar meaning is "stern," which implies a strict and serious disposition.
earnest
another word for eclectic