My girls and I were reading Mere Christianity by C.S. Lewis when the word colloquialism popped up.  Here is the sentence:

“In my talks, I used all the contractions and colloquialisms I ordinarily use in conversation.”  – C.S. Lewis in Mere Christianity. 

I asked my girls what the word colloquialism meant.

Here is my daughter’s guess:

Phrases and expressions used in normal conversation

She got it.  Here is Google’s definition:

a word or phrase that is not formal or literary, typically one used in ordinary or familiar conversation.

Colloquialism comes from the Latin prefix con, which became col before the letter l, and the Latin verb loquor, meaning, “I speak”.