In a Sense vs In Essence

In a sense (idiom) - in a way; in one way of looking at it
•    In a sense, computers have been a
      boon to society.
       In essence (idiom) - by nature;    
       essentially
•    The cat is, in essence, quiet
    and timid.

Cache vs Cash

Cache (noun) - a safe place to store supplies; anything stored or hidden in such a place

•    The hikers found a cache with some  
       cash and jewels.
      Cash (noun) - money, coins, bills;  
      currency
•    ATM machines dispense cash.

Source: Internet