This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. A preliminary discussion, especially a formal essay introducing a work of considerable length or complexity.

n. Prefatory remarks or observations.

n. A prefatory discussion; a formal essay or critical discussion serving to introduce and interpret an extended work.

n. A preliminary remark or observation; an introductory discourse prefixed to a book or treatise.

n. A preliminary observation: chiefly used in the plural, and applied to an introductory discourse prefixed to a book or treatise.

n. a preliminary discussion inserted at the beginning of a book or treatise

"Vives 'philosophical reflections on the human soul are mainly concentrated in De anima et vita, published in 1538, which provides the psychological underpinning for many of his educational ideas and can be characterized as a prolegomenon to moral philosophy."

introduction   

prolegomena   

prolegomenous