1643: Parasitic -B Jun 14, 2019

Although certain silent letters in English are normal, like a terminal E, others, like 'pterodactyl's' P, or even 'thumb's' B draw some more attention. This terminal B in many words is a remnant of something that was originally pronounced, such a in 'tomb'. The problem is that it is [m] is so similar a sound and these types of sounds at the end of the word anyway are often not aspirated, so not pronouncing a [b] makes little difference. In other words like 'thumb', the B was never pronounced even in Old English, but it got attached due to association to other words like 'dumb'. This is occasionally called a parasitic -b.
See more on 'thumb' here.