No, connection to earth does not define a neutral.
It is neutral because the vector sum of the "live" conductors is zero at that point.
Thanks Jim and Don. Appreciate
Part of the definition of a neutral point by Don:
midpoint on a single-phase, 3-wire system,
In UK, a single-phase supply to a building is always 2-wire for the current carrying conductors and designated designated live and neutral.
There are no three wire single phase systems
From Jim:
It is neutral because the vector sum of the "live" conductors is zero at that point.
If you take the vector sum of phase to neutral voltages on a three-phase system, yes it will be zero. The same on the midpoint of a single phase system where the two lives are 180 deg apart. Again zero for the vector sum of the voltages.
But if, as in UK, you have just a single-ended single-phase voltage, it is a non-zero sum.
But one is designated neutral.
Different countries. Different countries, different systems and I'm sure part of this is historical.
I have learned a lot from this forum on a number of topics.
Including the differences between the LV distribution systems between UK and USA.
You have 480, 277, 240, 208, 120, and possibly others.
For me, as a simple Brit, that seems just a bit overly complex or maybe unnecessarily complex.
In UK, LV distribution is 400V three phase, 230V single phase (phase to neutral of 400V) or sometimes just single-phase 230V.
With very few exceptions, residential service is single-phase 230V. All domestic equipment is rated to run on 230V. From phone chargers to washing machines and water heaters. And everything in between. A lost neutral from a centre-tapped 120-0-120 possibly resulting in overvoltage for some circuits isn't a problem we encounter.
As I mentioned earlier, the differences may be historical. And you work with what you have. The LV electrical distribution infrastructure for developed countries has been in place for very many years. Changing them this late in the game isn't an option.
But I like simple.