noun, noun which may take the genitive case particle 'no'
formula; prescribed form; established formality
Refers to a fixed, conventional form or procedure, often in formal or ceremonial contexts. Can be used as a noun or adjectivally with の.
結婚式の定式に従って進行した。
The ceremony proceeded according to the established formality of a wedding.
この書類は定式のフォーマットで作成してください
Please prepare this document in the prescribed format.
Compound of 定 (fixed, established) and 式 (ceremony, form, formula). The reading じょうしき is a rare alternative, possibly influenced by 常識 (common sense), but is not standard.