According to legal docs, obtained by TMZ, trademark applications have been filed for the phrases "Everything I Thought It Was" and "Everything I Thought It Was ... A Sonic film."

The reason that's relevant to JT and what appears to be a soon-to-be-announced album is the fact the attorney on record for this trademark app made a very similar, and telling, move a few years ago.

The trademark app for 'EITIW' was filed by an entity called TBTHC LLC -- and it's signed by C. Brandon Browning ... an attorney who certainly knows his way around the U.S. Patent and Trademark Office, as it pertains to Timberlake music projects.

Browning filed the trademarks for Justin's "Man of the Woods" album back in 2018 -- and now, here he is doing it again for "Everything I Thought It Was."

That's not the only huge clue -- Browning's filing comes just as JT himself is beginning to tease something with those exact initials -- 'EITIW' -- on his social media.

ICYMI, Justin recently scrubbed his entire Instagram page, and now, he has only 2 posts on his IG -- the 'EITIW' one, and another promoting his Friday night show in Memphis ... all of which leads fans to believe a sixth album is on the way.

As for the new trademark applications ... they're filling to use 'EITIW' for musical sound recordings, posters, soundtracks and merchandise -- basically, everything that goes with promoting, selling and performing new music.

Justin historically files all his trademarks under the LLC "Tennman Brands" ... and the new trademarks are under the LLC "TBTHC." Obviously, the "TB" could be an abbreviation for "Tennman Brands."

Anyway, the *NYSNC reunion might not be in the cards anytime soon, but Justin fans definitely have good reason to get excited about new solo music from him.