(verb) 1 to say, utter or exclaim something in delight or surprise. 2 to laugh or burble with joy esp. in surprise. 3 to communicate in an exuberant manner
xanthusiasm (noun), xanthucious (adjective), xanthuciously (adverb)
etymology: xantho-, a combining form meaning "yellow". It is thought that the word was first used to denote the happy mood evoked by a sunny day.
"The watermelon is square!" he xanthused.