In yesterday's crossword in THE NORTHERN ECHO, a clue was "Opt confusingly for bikini part". ??? The answer seemed obvious - the anagram of "opt" is top = part of a bikini. The answer published today is given as RUM. I can't see that and am assuming that the wrong clue was printed.
The answer to "Billet less than half" going across was QUARTER. The U was the middle letter to the "bikini" clue coming down through it, needing three letters.
Your google suggestion does indeed link "rum" and "bikini" but it doesn't explain the "opt confusingly" part of the clue.