We all realize English is a dynamic language, constantly adding words and changing meanings. The most common definition of gay has completely changed in my lifetime, and google has been added as both a noun and a verb. (Yes, it was a word before, but as googol, the number 1 followed by 100 zeros.)
But let’s examine the other side of the coin — how many words does English lose? Some words become obsolete and gradually fade away. But others hang on even though they are in the obsolete category. These are called “fossil words”. The website Daily Writing Tips defines fossil words as “artifacts from another era and survive only in isolated usage”. The most common “isolated usage” is being part of an idiom (a phrase established by usage as having a meaning not deducible from those of the individual words, such as “see the light”). For example, bated means “restrained or deducted”, but the only time you hear it today is in the idiom “wait with bated breath”. Another good example is yore, meaning “the far past”; today it’s only used in the expression “days of yore”. Ditto for loggerhead, with an original meaning of “blockhead”, but only heard today in the idiom “at loggerheads”. (It also helps a word to stay alive by having an animal — loggerhead turtle — named after it).
If this interests you, Daily Writing Tips gives 32 more examples at http://www.dailywritingtips.com/35-fossil-words/