Another de-facto standard stack manipulation word, TUCK places a copy of the top word under the second word. You can define it as follows:
: tuck ( x y -- y x y) swap over ;
TUCK is
not a standard word; it's just so useful that
everyone who needs it
defines it thus, and calls it the same. Many
implementations will also include it.
Compare NIP, DUP and OVER.