In Jain usage:

• Paishunya means backbiting, gossiping, or speaking ill of someone in their absence. ( jainbelief.com)
• Abhyakhyan means false accusation or wrongly blaming someone for a fault they did not do. ( jaingpt.org)

In simple words:

• Paishunya = slandering behind someone’s back
• Abhyakhyan = accusing someone falsely ( jainbelief.com)

These are both considered harmful speech-related faults in Jain ethics. ( jaingpt.org)