The phrase “common thread” in crosswords typically clues a word meaning a unifying idea or motif that runs through things, and the exact answer depends on the given letter pattern and grid location. Based on common crossword conventions, likely 9-letter candidates include MOTIFLINE (rare), THEMESONE (not standard), or INTERLACE (not a fit for “thread”). However, without the specific letter pattern from your puzzle, pinning the exact answer is tricky. If you can share:

• The grid pattern or the number of each row/column containing the clue
• Any known letters from crossing entries

I can narrow to the precise solution quickly. In the meantime, here are several high-probability 9-letter options that crosswords often use for “Common thread” or closely related clues:

• MOTIFLINE (conceptual but not common)
• THEMELOOP (not standard)
• THREADOF (too short)
• GISTOFALL (not standard)

If your clue is indeed in a Universal or NYT-style puzzle, the standard approach is to look for synonyms: motif, theme, central idea, throughline. The strongest single-word candidate that often appears for “thread” in a literary sense is THROUGHLINE (11) or THROUGH-LINE (with hyphen). For a 9-letter fill, THROUGHLYN is not valid, but THROUGHLINE is the right concept though length mismatch. Please share the intersecting letters or the puzzle context (publication/date), and the exact 9-letter pattern, and I’ll provide the exact answer.