Strike an enemy, adding your proficiency bonus to the damage. Moreover, if the attack hits, it deals an additional 1d6Psychic damage. This attack doesn't break concealment.
"Not breaking concealment" means that while solo and hiding, the wielder can attack their target without entering combat. This lets them get two attacks off before their opponent is aware of them, making it an excellent candidate for use in assassinating isolated NPCs.
Sword of Clutching Umbra, and 
Justiciar's Scimitar.
damage. This attack doesn't break concealment.
Action
1d6 (1~6) 
Attack roll
Range: Normal weapon range
Recharge: Short rest
, the wielder can attack their target without entering combat. This lets them get two attacks off before their opponent is aware of them, making it an excellent candidate for use in assassinating isolated NPCs.