platoon

Platoon comes from obsolete French plauton, a variant of peloton, which itself came from Middle French pelote plus the suffix -on.

The facts here don't trace a change in meaning, just the path of the word's spelling through French before it settled into English.

Platoon is a doublet of peloton — the two words descend from the same root but arrived in English by different routes. It's also worth comparing to pellet, which shares that same small-round-thing ancestry.