What word describes someone who speaks lots and says little, starts with long-, and takes six more letters to finish?
The answer is of course long-winded, but this would fit better on a gaming and puzzles sites.
The OED also provides long-lunged as a synonym of long-winded. Which one you want will depend on just where the other words in your crossword puzzle cross this one.
You won’t be able to use the synonyms long-breathed, long-tongued, or longiloquent because they have too many letters for your boxes, while longsome has too few.