Re: My favorite silent English letter is:

[mertserger]

Maybe other British English speakers will disagree with me, but I would never drop the "o" at the beginnging of "opossum" but then it isn't a word I use very much either.

[runrig]

The "o" completely disappears in the phrase "play possum" :-)

[mertserger]

But there is no silent O in "possum" though it is possible there might be a missing one, if you consider possum=opossum. It is quite common for words to lose letters over time, like how the Latin "fenestra" became the French "fenêtre". Can you tell I do tech support for a dictionary?

[runrig]

See my note elsewhere in this thread.

[LanX]

checking WP reveals that opossums and possums belong to different families.

So probably it's a false example.