The most common and most likely answer to this crossword clue is the 7 letter word CLIP-ON
I've seen this crossword clue in The Guardian
C
L
I
P
-
O
N
Buddy explains!

The straight part
We know that "Tie" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tie = clip-on.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 CLIP-ON mean?
CLIP-ON noun- Any item that attaches to something by means of a clip.
- That attaches to something by means of a clip.