In Brazil, pieces of legislation are usually referred to by either a number (e.g. lei n° 6.404/76) or a name (e.g. Lei das SA). When translating into English, use Law when mentioning the number (e.g. Law No. 6,404) and Act when mentioning the name (e.g. Corporation Act).
There are multiple definitions - click on the translation that matches your context.
(before a noun) relating to the legal profession, the courts or to a particular legal system
He works for a law firm.
a specific rule within a particular country, area or community, recognised as binding and enforced by an authority; a rule enacted by the legislature
A new law on civil partnerships will be debated in parliament later today.
relating to the area of knowledge that deals with systems of rules
a law degree