According to the Oxford Dictionary, you can use far as an adverb either about distance (meanings 1 and 2), time (meaning 2) or as an adverb of degree (meaning 3), meaning
- By a great deal.
With meaning 3, you cannot apply it directly to an adjective in the same way that you can say very good. You can only ever apply to a comparative (the -er version of an adjective), for example:
His new car is far faster than the last one.
If you want to use it with an adjective that you can't make a comparative with, you should use more and the adjective, for example:
This word is far more common.
To answer Dan's comment about the expression "not far wrong", you can also use far
to modify adverbs, and the word wrong
can be an adverb. The expression was probably initially used in sentences like this:
If you follow my advice, you won't go far wrong.