1. Characterized by dignity and propriety
   "Her staid demeanour was perfect for the formal occasion";
   - sedate
    
2. Excessively conventional and unimaginative and hence dull
   "why is the middle class so staid, so utterly without a sense of humour?";
   - stodgy, stuffy

Sounds like: staff, staid

Derived forms: staider, staidest

See also: button-down, buttoned-down [US, informal], conservative, conventional, decorous