I missed this Guardian article earlier this month, but if you haven't seen it yet, it's worth a read. It attracted over 3,500 readers' comments. It's about how some of the current spelling and pronunciation in today's English came about because of pronunciation mistakes and confusions in the past.
Adder, apron and umpire all used to start with the letter n. People got so used to saying a nadder, a napron etc, that they thought the n was part of the indefinite article. The process of metathesis, where sounds are transposed, is responsible for today's wasp and bird. Previously one said waps and brid. Syncope is the process of losing sounds, so Woden's day became Wednesday and the letter t is not pronounced in Christmas. The opposite process, when sounds inadvertently get added while pronouncing a word is called epenthesis. Empty used to be emty and thunder thuner. The l of folk, talk and walk used to be pronounced, but over time the l began to sound more like a w. L after a vowel is pronounced with the back of the tongue raised, and w is a very similar sound, it's just that the tongue is raised a bit higher. The l to w process is known as velarisation.
For more examples, and the full article, see here.