According to the Oxford dictionary:
larceny /ˈlɑːs(ə)ni/ noun
theft of personal property.
theft /θɛft/ noun
the action or crime of stealing.
What is the difference between the two? Can they be used interchangeably?
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These (from Lexico) are broad rather than precising definitions. In British law, a tightening of terminology to give a more precise definition of what counted as theft was made in the 1960s. The offence of 'larceny' was dropped in 1969, so the term is essentially obsolete in the UK (though less precise usages will doubtless occur, using it as an old-fashioned synonym of 'theft').
Different jurisdictions will have more precise definitions for 'larceny', 'theft' etc, which will largely overlap with those of other jurisdictions, but may well conflict in certain areas.
Wikipedia gives more precision:
larceny Law ...
Larceny is a crime involving the unlawful taking or theft of the personal property of another person or business. It was an offence under the common law of England and became an offence in jurisdictions which incorporated the common law of England into their own law (also Statutory law), where in many cases it remains in force.
The crime of larceny has been abolished in England and Wales, Northern Ireland, and the Republic of Ireland due to breaking up the generalised crime of larceny into the specific crimes of burglary, robbery, fraud, theft, and related crimes. However, larceny remains an offence in parts of the United States, Jersey, and in New South Wales, Australia, involving the taking (caption) and carrying away (asportation) of personal property.