The answer to the crossword puzzle is 'was'. The term 'third word in many limericks' refers to the fact that the third word of many limericks is usually 'was'. This is because the traditional form of a limerick consists of five lines, with the first, second and fifth lines rhyming and the third and fourth lines rhyming. The third word of the limerick is often 'was' as it is a common word that rhymes with many other words.