Real Dictionary

vat
countable noun: A vat is a large barrel or tank in which liquids can be stored.
uncountable noun: VAT is a tax that is added to the price of goods or services. VAT is an abbreviation for ' value added tax'.

VAT in American English
a large container for holding liquids, as those to be used in a manufacturing process or those to be stored for fermenting or ripening
to place or store in a vat
value-added tax
abbreviation
noun: a large container, as a tub or tank, used for storing or holding liquids
transitive verb: to put into or treat in a vat

vat in British English
abbreviation for: value-added tax: a tax levied on the difference between the cost of materials and the selling price of a commodity or service
noun: a large container for holding or storing liquids
verb: to place, store, or treat in a vat

Vat. in American English
Vatican

Vat. in British English
abbreviation for: Vatican
noun: the palace of the popes in Rome and their principal residence there since 1377, which includes administrative offices, a library, museum, etc, and is attached to the basilica of St Peter's