1.
faithlessness; insincerity; dishonesty
Lack of sincerity, honesty, or faithfulness. Often used to describe someone who is unfaithful in a relationship, or who acts dishonestly or without integrity.
不実 is the opposite of 誠実 (sincere, faithful). It functions both as a noun and as an adjective with な. In literary and formal contexts, it often carries the specific nuance of infidelity or betrayal of trust.