The most common and most likely answer to this crossword clue is the 6 letter word ABOARD
A
B
O
A
R
D
More clues leading to the result ABOARD
Buddy explains!

The straight part
We know that "smuggled thus" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case smuggled thus = aboard.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 ABOARD mean?
ABOARD adverb- On board; into or within a ship or boat; hence, into or within a railway car.
- On or onto a horse, a camel, etc.
- On base.
- Into a team, group, or company.
- Alongside.
- On board of; onto or into a ship, boat, train, plane.
- Onto a horse.
- Across; athwart; alongside.