A.T. Robertson Commentary Luke 22:17

"And he received a cup, and when he had given thanks, he said, Take this, and divide it among yourselves:" — Luke 22:17 (ASV)

He received a cup (δεξαμενος ποτηριον). This cup is a diminutive of ποτηρ. It seems that this is still one of the four cups passed during the passover meal, though which one is uncertain. It is apparently just before the formal introduction of the Lord's Supper, though he gave thanks here also (ευχαριστησας). It is from this verb ευχαριστεω (see also verse 19) that our word Eucharist comes. It is a common verb for giving thanks and was used also for "saying grace" as we call it.