Real Dictionary

tax
variable noun: Tax is an amount of money that you have to pay to the government so that it can pay for public services.
verb: If something taxes your strength, your patience, or your resources, it uses nearly all of them, so that you have great difficulty in carrying out what you are trying to do.
verb: When a person or company is taxed, they have to pay a part of their income or profits to the government. When goods are taxed, a percentage of their price has to be paid to the government.

tax in Accounting
Tax is an amount of money that you have to pay to the government so that it can pay for public services such as roads and schools.

tax in American English
to determine the value of; assess
intransitive verb: to levy taxes
noun: a sum of money demanded by a government for its support or for specific facilities or services, levied upon incomes, property, sales, etc.
transitive verb: to demand a tax from (a person, business, etc.)

tax in British English
to levy a tax on (persons, companies, etc, or their incomes, etc)
noun: a compulsory financial contribution imposed by a government to raise revenue, levied on the income or property of persons or organizations, on the production costs or sales prices of goods and services, etc

tax in Retail
Tax is an amount of money that you have to pay to the government so that it can pay for public services such as roads and schools.

tax- in American English
combining form