Actually in my family we call it Sunday Lunch....so i suppose it still holds there.
In my actual life, i only eat one meal - in the evening, so i suppose that since i have no need to distinguish between them, i could just call my evening meal 'meal' or 'foodtime' and be done with it.
I presume everyone calls it whatever their parents/carers call it. I doubt anyone wakes up one morning and says 'Hmm, I know what i'll call dinner, just to fuck with everyone else - i'll call it tea. That'll piss everyone off!'