abacus abacus /ˈæbəkəs/

noun

1. A calculator that performs arithmetic functions by manually sliding counters on rods or in grooves  ( abacus )
   a calculator that performs arithmetic functions by manually sliding counters on rods or in grooves
    As a child, he learned arithmetic on an abacus before using a calculator.
   As a child, he learned arithmetic on an abacus before using a calculator.
   
   
2. A tablet placed horizontally on top of the capital of a column as an aid in supporting the architrave  ( abacus )
   a tablet placed horizontally on top of the capital of a column as an aid in supporting the architrave
    Historically, architects used an abacus to support intricate structures atop columns.
   Historically, architects used an abacus to support intricate structures atop columns.