Search string which is not suffix or prefix of another word

Many a times we need to find the count of a particular word in a file, but this word can also be a prefix or suffix to another word. In order to find the word as a whole,

F 'STRING' WORD;

Here we will get only the occurences of the word 'STRING' in the file or code and no other words like 'UNSTRING' or 'STRINGS'