Why is there a b at the end of the word thumb?

The "b" at the end of the Word "thumb" is a remnant of its Old English origin, where the Word was spelled "þūma" (with the "b" sound later becoming silent). Over time, as the English language evolved, certain letters became silent in pronunciation while remaining in spelling. This phenomenon is common in English, where historical spellings often preserve sounds that are no longer pronounced. Thus, the "b" remains in "thumb" as part of its linguistic heritage.