My teacher once said when you speak you have to say it clearly because sometimes people misinterpret it. Especially in writing when you write you have to spell it correctly because once you misspelled it the meaning will be change. So here are some examples of words that when you change the first letter it will also change the meaning. My reference is dictionary.com.
One letter makes all the difference
to decline to accept (something offered).
to become decomposed; rot.
not proud or arrogant; modest.
to give up or over; relinquish or resign.
amiably gentle or temperate in feeling or behavior toward others.
to exercise (power, authority, influence, etc.), as in ruling or dominating.
great warmth of feeling; fervor; passion.
having or showing acute mental discernment and keen practical sense; shrewd.
being within; inside of anything; internal; inner.
situated before or at the front of; fore (posterior).
a leafy, shady recess formed by tree branches, shrubs, etc.
obscene; grossly indecent.
to put off to a later time; defer; postpone.
shelter or protection from danger, trouble, etc.
to bungle or blunder awkwardly; muddle.
vo ri-doos, –dyoos
to bring down to a smaller extent, size, amount, number, etc.
living in a state of nature; not tamed or domesticated.
to remove the fuze from (a bomb, mine, etc.).
to derive as a conclusion from something known or assumed; infer.