• 祝日しゅくじつ — national holiday
• 祝儀しゅうぎ — celebratory gift (esp. wedding money)
• 祝福しゅくふく — blessing
• 祝賀会しゅくがかい — celebration party
• 祝いいわい — celebration; congratulatory gift
• 祝辞しゅくじ — congratulatory address
• 祝祭しゅくさい — festival; celebration

The left radical 礻 (しめすへん) evokes a ritual altar; the right side relates to declaration. Together they suggest offering thanks or prayers, which broadened to general celebration.

友ともだちの結婚けっこんを祝いわいました。
I celebrated my friend’s wedding.

来週らいしゅうは 祝日しゅくじつです。
Next week is a national holiday.