Q. 142. What are the sins forbidden in the eighth commandment?
A. The sins forbidden in the eighth commandment, besides the neglect of the duties required, are, theft, robbery, man-stealing, and receiving any thing that is stolen; fraudulent dealing, false weights and measures, removing landmarks, injustice and unfaithfulness in contracts between man and man, or in matters of trust; oppression, extortion, usury, bribery, vexatious lawsuits, unjust inclosures and depopulations; ingrossing commodities to enhance the price; unlawful callings, and all other unjust or sinful ways of taking or withholding from our neighbour what belongs to him, or of enriching ourselves; covetousness; inordinate prizing and affecting worldly goods; distrustful and distracting cares and studies in getting, keeping, and using them; envying at the prosperity of others; as likewise idleness, prodigality, wasteful gaming; and all other ways whereby we do unduly prejudice our own outward estate, and defrauding ourselves of the due use and comfort of that estate which God hath given us.
Gambling and Lotteries are a violation of the 8th Commandment.
Also see WSC #73-75 and WLC #140-142.