The most common and most likely answer to this crossword clue is the 6 letter word NESSIE
N
E
S
S
I
E
More clues leading to the result NESSIE
- Is seen when swimming
- Scottish monster is seen swimming!
- Monster, one in northerly German city
- She is sensibly hiding return of monster …
- Reclusive Scot is seen photoshopped
- Monster that is spotted south of headland
- Monster is seen swimming
- Creature is seen possibly
- Scottish monster’s head, that is...
- Monstrous creature periodically incenses Indo-European
Buddy explains!

The straight part
We know that "monster" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case monster = nessie.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.