Why microwaves are called microwaves ?

Question

microwaves have wavelength in range of 1mm to 30 cm then from where the the term MICROWAVE comes from .....

Answer 1

Micro is defined as millionths as in millionths of a meter.  Microwaves are wavelengths of light that are millionths of a meter long.

Answer 2

Actually I have no idea, but I'll have a guess.

Radio started with an ability to create only low frequencies, by modern standards. As you suggest, wavelengths are the thing.

As people started to be able to build equipment with higher & higher frequency wavelengths got shorter.

3MHz - 30Mhz was branded "Short wave" when it seems short compared to the previous.

After a while when you get to 300MHz & up what would you call them?

After "short" "micro" does not seem all that unreasonable.

I suspect your suspicion is also right, it has not much to do with standard units of deci, milli, micro, &c.

Then again, I could be wrong.