A four letter word meaning the foundation of something is base.
It means that something can be changed after it is created. Immutable means that it can't be changed.
A word for something that children play with is toy.
The letter f can be changed to g to form the word ginger.
Originally means something before was changed.
altered, renewed, evolved,
participants means someone who participates in something. for instance, children are participants in school because they participate in it. and participate means to take part in something.
Cooking something, you can never uncook something...
place something in an envelope together with a letter