an expert at calculation (or at operating calculating machines)
"After years of working in accounting, she became a true calculator when it came to balancing complex ledgers without any errors."
a small machine that is used for mathematical calculations; can be mechanical or electronic
"She pulled out her calculator to quickly check if the discount at the grocery store was actually what she thought it was."
A mechanical or electronic device that performs mathematical calculations.
"I pulled out my calculator to double-check the tip amount on the restaurant bill before leaving."
In plain English: A calculator is a tool that quickly adds, subtracts, multiplies, and divides numbers for you.
"She used her calculator to quickly add up the total cost of her groceries."
Usage: Use "calculator" to refer to a handheld electronic device used for performing arithmetic operations like addition and multiplication. Do not use it to mean a person who calculates figures, which should instead be described as an accountant or mathematician.
The word entered English from the Latin calculātor, originally referring to a mathematician or astrologer who performed calculations. Its modern meaning as a machine for computing numbers developed later in the language.