Ci

1 of 2

abbreviation (1)

1
cirrus
2
curie

CI

2 of 2

abbreviation (2)

1
cast iron
2
certificate of insurance
3
Channel Islands
4
confidential informant; criminal informant

Browse Nearby Words

chytridiosis
Ci
CI
See all Nearby Words

Cite this Entry

“Ci.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/Ci. Accessed 25 Oct. 2025.

Copy Citation

Share

Medical Definition

CI

abbreviation
chemotherapeutic index

Legal Definition

CI

abbreviation
certificate of insurance; cost and insurance

More from Merriam-Webster on Ci

Britannica.com: Encyclopedia article about Ci

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Popular in Grammar & Usage

See More

'Affect' vs. 'Effect'

Plural and Possessive Names: A Guide

Using Bullet Points ( • )

'A' or 'an'? What about before 'h'? An Indefinite Article Guide

The Difference Between 'i.e.' and 'e.g.'
See More

Popular in Wordplay

See More

8 Real (and Perceived) Redundant Words

17 Words for Dog Breeds

Ten More Words from Taylor Swift Songs

And So It Begins: 9 Words for Beginnings

Why do we 'bury the lede?'
See More

Popular

See More

'Affect' vs. 'Effect'

8 Real (and Perceived) Redundant Words

17 Words for Dog Breeds
See More

Games & Quizzes

See All
Play Quordle: Guess all four words in a limited number of tries. Each of your guesses must be a real 5-letter word.
Quordle Can you solve 4 words at once?
Play Blossom: Solve today's spelling word game by finding as many words as you can using just 7 letters. Longer words score more points.
Blossom Pick the best words!
Play Missing Letter: a crossword with a twist. Each of the 25 puzzle words start with a different letter of the alphabet. Which letter is missing?
The Missing Letter A daily crossword with a twist
different halloween monsters in silhouette
A Monstrous Vocab Quiz Words That Go Bump in the Night
See All