The spelling of the word "Sumption" follows the traditional English pronunciation rules, despite featuring an unusual combination of letters. It is pronounced /ˈsʌmpʃən/, with the first syllable being emphasized and the "u" sound closer to "uh" rather than "oo". The "mpt" cluster is also pronounced as "mpsh", hence the "sh" sound in the end. While the spelling might confuse some native and non-native speakers alike, understanding the pronunciation rules can help to make sense of it.
The surname Sumption is of English origin and is believed to have derived from a medieval personal name Simon. The name Simon itself has Hebrew origins and comes from the Hebrew name Shim'on, meaning he has heard. Over time, this name transformed into various forms and spellings, including Simonds, Simons, and Sumption. The suffix -tion on Sumption is likely a variant spelling of -son, which means son of Simon. Thus, Sumption would suggest son of Simon.