Attention given to another's wellbeing at cost to oneself. Care is measured in what it displaced, not in what it said.
Old English caru/cearu (sorrow, anxiety, grief; also solicitude), from Proto-Germanic *karo; despite the resemblance, it is not the same root as Latin cura (the ancestor of 'cure' and 'curate') — two separate words that ended up looking alike.
Attention given to another's wellbeing at some real cost to the giver — measured, in this house, by what it displaced rather than by what it said.