The most common and most likely answer to this crossword clue is the 5 plus 4 letter word THIRD RATE
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The straight part
We know that "rubbish" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rubbish = third rate.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 THIRD RATE mean?
THIRD RATE noun- A British ship-of-the-line with 64 to 80 guns divided across two gun decks.
- Of lesser value or quality than second-rate.
- Describing a British ship-of-the-line with 64 to 80 guns divided across two gun decks.