The most common and most likely answer to this crossword clue is the 3 letter word FRO
I've seen this crossword clue in The Times
F
R
O
More clues leading to the result FRO
Buddy explains!

The straight part
We know that "to? The opposite" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case to? the opposite = fro.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 FRO mean?
FRO adverb- From; away; back or backward.
- A hairstyle characterized by a tightly curled locks and a rounded shape.