I didn't catch that.

I Pronoun

— The person who is speaking or writing I am writing this, and you are reading it.

I Noun

— The ninth letter or the alphabet; previous H, next J. I is a vowel.

I Symbol

— A symbol meaning first, as in "George I" (which is said as "George the first"). — The symbol for iodine on the periodic table of elements. — The symbol for electrical current.

I Number

— This is the roman numeral for one (1). It may be written as I or i.

i Noun

— The ninth letter or the alphabet; previous H, next J. I is a vowel.

didn't verb

— did not (negative auxiliary)

catch Noun

— A catch is something that is caught, like the fish a fishermen catches. My dad brought home a good catch of trout today. — A catch is old time word for a song. We sang a catch by Purcell.

catch Verb

— When you catch something, you stop and hold it. Can you catch a fish in your hands with no fish net? They caught the bad guys and locked them up.

that Determiner

— Used to show which thing we are talking about; used with things that are not close to the speaker. Give me that book, not this one. Give me that, not this. That dog is hungry.

that Subordinator

— used to link a subordinate clause to a main one You said that you liked me. Give me the book that I dropped.