>>9795083>>9795085Silent letters are often a relic of previous pronunciation -- such is the case with the "k" in "knight".
The "b" in "subtle" is no exception, though in a sort of round-about way.
"subtle" originated from Latin subtilis, where "sub" is the prefix meaning "under" that we still use today. However, English took the word from Old French sotil, soutil, subtilas. The different spellings in Old French indicate that there were varying pronunciations, probably due to different dialects.
