Larceny is the crime of stealing — taking someone else’s property on purpose. It is a lawyer’s word more than a kitchen-table word. In news and in court, especially in American English, you will hear petty larceny (stealing something of small value) and grand larceny (stealing something of high value). In everyday British English people more often say theft or stealing; larceny sounds like a charge on a police report. Though actually, some places have folded the old larceny laws into a broader theft law, but the word is still widely understood as “the stealing crime.” It is formal. You would not tell a child “that’s larceny” over a biscuit. The act is larceny; the person is a thief, or someone charged with larceny — not “a larceny.”