Purist = a person who insists on absolute adherence to traditional rules or structures, especially in language or style.

stickler, traditionalist.

Most purists are fans of traditions and traditional rules. To be a purist is to be a kind of a perfectionist.

• If you are a language purist, it upsets you to hear someone using bad grammar.
• A baking purist might feel that cookies made without a certain brand of chocolate chips are vastly inferior.

Puritan = person who is strict in morals and religion, who looks upon some kinds of fun and pleasure as sinful.

• The Puritans were English Reformed Protestants in the 16th and 17th centuries who sought to ‘purify’ the church of England.
• The Puritans do not approve of the theatre because of the pleasure that seeing plays gives to the audience.
• Puritanical readers will be horrified by the amount of bad language that the book contains.