Seam and Seem are homophones. They sound identical, which in some way is English’s way of laughing at us. They look as though they should be related, and for a moment they even share Old English soil, but beneath that overlap they are doing entirely different jobs.
A seam is unapologetically physical. It comes from Old English sēam, and before that Proto-Germanic saumaz, meaning a stitched joint. Its relatives appear across the Germanic languages doing the same honest work: Old Norse saumr, German Saum. A seam joins real things. You can tug on it. You can blame it when your trousers fail you in public. If a seam gives way, the evidence is immediate and embarrassing.
Seem, by contrast, comes from Old English sēman, from Proto-Germanic sōmjaną, meaning to appear or to give an impression. Nothing is actually joined when something “seems” true. Your mind stitches together a conclusion and hopes no one tugs at the thread. From the beginning, seem has lived in the realm of appearances and assumptions.
In short:
Seam holds fabric together.
Seem holds ideas together.
So while they sound the same and come from the same dirt, they are not siblings. They aren’t even cousins. They’re acquaintances who confuse people at parties.
Tom Bont's Silver Key 