Even heavy water would only weigh 1.112 grams per cc (at 4 degrees Celsius).

The molar mass of heavy water is 20.0276 versus 18.01528 for regular water.

Not by definition: a kilogram is defined as the exact mass of a lump of iridium-platinum alloy sitting in a vault in Paris (well, Sèvres). But the kilogram was designed to be the weight of a liter of water at its melting point, and then later 4°C (where water achieves maximum density).

One cubic centimetre of water at 4 degrees Celsius used to define one gram (or more precisely one litre -> one kilogram, which comes out to be the exact same thing) [1], [2].

Although 1 cm^3 of water is still pretty damn close to 1g.

[1] https://en.wikipedia.org/wiki/Grave_%28unit%29

[2] https://www.youtube.com/watch?v=ZMByI4s-D-Y (around 1:50, and actually the whole video is excellent)

Yes it is sorry and thanks, I knew that 1 ml = 1 but I did not check out my incorrect instinct re volume. I was thinking of 5 grams to a teaspoon, intuitively 5 cc seems to me, much bigger than 1 small teaspoon. Still surprising to me though, how 5 grapes can fit on a teaspoon ?

Only at one specific temperature (4 degrees C).