The most common and most likely answer to this crossword clue is the 6 letter word WOOLLY
I've seen this crossword clue in The Sunday Telegraph
W
O
O
L
L
Y
More clues leading to the result WOOLLY
Buddy explains!

The straight part
We know that "Vague/description of mammoth?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case vague/description of mammoth? = woolly.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 WOOLLY mean?
WOOLLY noun- A sweater or similar garment made of wool.
- A sheep not yet shorn.
- A piece of woolwork.
- Made of wool.
- Having a thick, soft texture, as if made of wool.
- (of thinking, principles, etc.) Based on emotions rather than logic.
- Unclear, fuzzy, hazy, cloudy.
- Clothed in wool.
- A woolly back; someone from the area around Liverpool, not from Liverpool itself.