Speaking or performing without preparation

Extempore: This word means speaking or performing without preparation. Pilfering: This word refers to stealing small items, often in a petty or sneaky manner. Preamble: A preamble is an introductory statement, typically found in a document or speech. Plagiarism: This is the correct one-word substitute. Plagiarism refers to the act of taking someone else's work or ideas and presenting them as your own. Therefore, "Extempore" is the most appropriate one-word substitute for the given group of words