Thankful, grateful, well-pleasing. From eu (well) + charizomai (to show favor) — one who recognizes and responds to grace with gratitude. The root gives us 'Eucharist' — the great thanksgiving meal of the church. Used by Paul as a direct command: 'Be thankful' (eucharistoi).
Eucharistos is not a personality trait but a command and a discipline. Paul orders: 'Be eucharistoi' (Colossians 3:15). Gratitude is the proper response to grace — indeed, ingratitude is one of the marks of rebellion in Romans 1:21. The Eucharist (Lord's Supper) takes its name from this word, making every communion a school of thanksgiving. To be eucharistos is to see all of life as gift.