to worry, be anxious: to be gripped by fretful, distrustful concern about one's needs or circumstances
This is the fearful, inward fretting that Jesus repeatedly forbids. It is not planning or honest work: Jesus points to birds that gather food and flowers that flourish, so the target is not activity but the dread that God will not provide. Worry of this kind borrows tomorrow's trouble and lives as though the Father were absent.
Whether the anxiety is about food, drink, and clothing, or about what to say when dragged before authorities, it is the same posture of heart. The New Testament ties it directly to weak faith: the person who worries this way is the one of "little faith." The cure it offers is not indifference but trust, whether in the Father's provision, the Spirit's help, or answered prayer.
This worry can also spill out of the mind into restless, driven busyness. Martha is described as anxious and troubled about many things, her inner unrest showing up as outward bustle, which is why some readers hear in this word both a worried heart and the frantic activity it produces.