The most common and most likely answer to this crossword clue is the 11 letter word MOUNTAINOUS
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Buddy explains!
The straight part
We know that "Towering" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case towering = mountainous.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 MOUNTAINOUS mean?
MOUNTAINOUS adjective- Having many mountains; characterized by mountains; of the nature of a mountain; rough (terrain); rocky.
- Resembling a mountain, especially in size; huge; towering.
- (of a problem or task) Very difficult.
- Inhabiting mountains; hence, barbarous.