serious, dull, or old-fashioned
staid - sober
Something ‘staid’ is considered boring, unchanging, or rigidly conventional. While oftentimes the word is used negatively to express stuffiness or an aversion to change and risk-taking, it can also be used in a more positive sense. For example, something staid may be dull, but nonetheless dignified and admirably restrained.
The culture within the company is very staid, which is why there is little room for free-thinkers or innovation.
The politician’s uplifting and energetic speech came as a surprise. She is normally known for her staidness.
Peter had a staidly conventional rural upbringing, which meant that he struggled when he moved to New York.