The most common and most likely answer to this crossword clue is the 7 letter word CARRIER
I've seen this crossword clue in The Guardian
C
A
R
R
I
E
R
Buddy explains!

The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CARRIER mean?
CARRIER noun- A person or object that carries someone or something else.
- A carrier pigeon.
- A person or company in the business of shipping freight.
- A signal such as radio, sound, or light that is modulated to transmit information.
- A mobile network operator; wireless carrier.
- A certified airline.
- That which drives or carries.
- A catalyst or other intermediary in a chemical reaction.
- A person or other organism that has a genetic trait, mutation or infection liable to cause a disease, but displays no symptoms.
- Charge carrier
- A liquid or gas used as a medium for another substance.