A tool or device used to make creases or folds in paper, fabric, or other materials.
Agent noun from 'crease' (to fold or wrinkle) plus the suffix '-er' denoting an instrument or person that performs the action. Became common in printing and bookbinding industries in the 19th century.
Professional bookbinders use special metal creasers to make perfectly sharp folds before cutting pages—the crease actually weakens the paper intentionally so it tears cleanly rather than crumpling.
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