Surreptitiousnesses, spelled /ˌsʌrəpˈtɪʃəsnəsɪz/, is a lengthy word with 18 letters that derives from the root word, surreptitious. The word means to behave quietly or secretly to avoid detection. The suffix -ness denotes the state or quality of the root word, while the plural suffix -es indicates there is more than one instance of surreptitiousness. The complex spelling of the word may be challenging to learn, but it highlights the intricacy of the English language and how it evolves over time.