what does 'ness' mean mummy?!

[OTgirl]

My 3.6 yr old dd would like to know what the word 'ness' means when added to words like 'dark', happy, gentle etc. I know when added to a word beginning it is a noun but I'd appreciate some help as she's really interested in the ending. Can anybody give me a nice simple explanation please?

have a look here , here and here

happy reading and explaining

Thanks for those links SSS. Still beyond me as far as giving an explanation but dd now knows that a word ending is called a suffix and is so happy with her new word and word endings such as 'er' 'ing' 'ly' and 'fuls's that I'm hoping she's forgotten that she wanted to know the meaning of 'ness'! It's a long time since I did english grammar and sentence construction!