In Forth, not just new words - everything (except the stacks, I think) - as if in C you could redefine not only every reserved word but every symbol - (, ), +,

In Forth, not just new words - everything (except the stacks, I think) - as if in C you could redefine not only every reserved word but every symbol - (, ), +, *, ->, %, &, [,],{,},# = etc etc. Also there are 'defining words' (akin to typedef, struct, enum etc) and you can define new defining words... And so turn Forth into any other language you wanted, if you were crazy enough..