The most common and most likely answer to this crossword clue is the 7 letter word MUFFLER
M
U
F
F
L
E
R
Buddy explains!

The straight part
We know that "neckwear" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case neckwear = muffler.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 MUFFLER mean?
MUFFLER noun- Part of the exhaust pipe of a car that dampens the noise the engine produces.
- A silencer or suppressor fitted to a gun.
- A type of scarf.