The Shared History of Dissimilar Words
Sometimes words that share a history don't do so in an obvious way, and we might not even connect them because we encounter them in different contexts.
Incumbent, succumb, and recumbent all share the Latin root cumbere, which means "to lie down."
Incumbent, which means "a person who holds a particular office or position" in English, comes from the Latin word meaning "to lie down on" – in other words, to possess.
Succumb, which can mean "to stop trying to resist something" or "to die," comes from the Latin word that meant "to fall down" or "to yield."
Recumbent means "lying down"; its Latin ancestor meant "to lie back" or "to recline."
There are also some very rare English words that show a family resemblance: cumbent and decumbent are synonyms of recumbent; accumbent was used to describe the way Romans sat at table to eat and in botany to describe how some parts of plants lie against others.
P.S. Reading all these cumbs may put you in mind of cucumbers, but the word is unrelated.