Word forms: plural prefixes1. countable nounA prefix is a letter or group of letters, for example 'un-' or 'multi-', which is added to the beginningof a word in order to form a different word. For example, the prefix 'un-' is added to 'happy' to form 'unhappy'. Compare affix and , suffix.
2. countable nounA prefix is one or more numbers or letters added to the beginning of a code number to indicate, for example, what area something belongs to.
To telephone from the U.S. use the prefix 011 33 before the numbers given here.
I soon learnt to read the licence plates' prefixes.