ceremonious
Ceremonious (adj) means Done in the proper formal way, following the usual customs or rules for an occasion.
Etymology
A learned borrowing from Middle French cérémonieux (also modern French cérémonieux), or taken directly from its source, Latin caerimōniōsus, plus English -ous (a suffix forming adjectives from nouns, showing the presence of a quality, typically in abundance). Caerimōniōsus derives from Latin caerimōnia ("awe, reverence, veneration; sacredness, sanctity; religious ceremony, ritual"), possibly ultimately from Proto-Indo-European *kʷer- ("to build, make; to do"), plus -ōsus (a suffix meaning 'full of, overly', forming adjectives from nouns). On the surface it can be analysed as ceremony + -ous.