In Sanskrit, yathi refers to an arrangement of syllables. In addition to pRAsa (rhyming words), Dikshithar has exquisitely crafted two kinds of yathis in his kRitis.
The Gopuccha yathi, as the name suggests, in shaped like a cow's tail. The sequence starts with a compound word, and progressively shorter, yet meaningful root words. There are atleast three examples of Gopucha yathis found in Dikshithar kritis.
In the majestic Anandabhairavi composition tyAgaraja yOga vaibhavam, the pallavi ends with a gopuccha yathi:
In 'mAyE tvam yAhi' set to the rare rAga tarangiNi, there is a shorter gopuccha yathi:
Yet another example of a gopuccha yathi can be found in the auspicious sRI rAga kRiti 'sRI varalakShmI':
The words in sRotovaha yathi are arranged in short to long order, like a flowing river. The example of this construct is found, again, in 'tyAgarAja yOga vaibhavam':
.. Phew! Anyone who read the last word in one go deserves a pat on the back.
Considering a viLamba rUpaka tALa kRiti like this, only a genius like Dikshithar could pull off such a feat.