verb/de.sɛ.ʁe/
to loosen (knot, belt, etc.); to unclench (teeth); relax (grip); release (brakes); to space out; to ease, relax; to come loose; to slacken
“Tu devrais desserrer ta cravate si tu ne te sens pas bien.” — You should loosen your tie if you don't feel well.
From dé- (“undo”) + serrer (“to tighten”).