Three letter words beginning with the letter I include “ice,” “ill,” “ins,” “ion,” and “its.” These three letter words are often used as part of compound words or to form more complex sentences. For example, the word “ice” can be combined with other words to create phrases such as ice cream, ice skating, and ice age. The word “ill” is commonly used in idiomatic expressions such as ill at ease, under the weather, and out of sorts. The word “ins” is often used to shorten longer words like inside or instigate. Finally, the words “ion” and “its” are commonly used in various scientific terms like emission and initiative respectively.