I wondered about the spelling of a word recently. Here is the answer I found.
The phrase “push the envelope” means to exceed, or try to exceed, established boundaries, limits, rules, etc.
The “envelope” is spelled and pronounced the same as that thing a letter arrives in.
However, if you omit the last “e,” you change the pronunciation and the word becomes a verb instead of a noun.
To “envelop” is to “wrap up,” “surround” or “conceal.”
There’s no such thing as “push the envelop.” That’s pushing too far.
The phrase was popularized by Tom Wolfe’s “The Right Stuff,” published in 1979. Before that it was rarely encountered outside aviation circles, where the “flight envelope” referred to capabilities and limits of aircraft. The job of test pilots was to push the envelope, sometimes was disastrous results.
A similar use of “envelope” also can be found in mathematics, but I stink at math, so we’ll leave it at that. I was an English major. I let others do the math.