The most common and most likely answer to this crossword clue is the 8 letter word MOUTHFUL
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Buddy explains!
The straight part
We know that "a small portion/a big word" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a small portion/a big word = mouthful.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 MOUTHFUL mean?
MOUTHFUL noun- The amount that will fit in a mouth.
- Quite a bit.
- Something difficult to pronounce or say.
- A tirade of abusive language (especially in the term “give someone a mouthful”)
- Bombastic or awkward.