Definition - A verse or a sentence in which each successive word has:
(1) One more syllable than the previous word or
(2) One more letter than the previous word.

Example -

(1) No effort continues unrewarded (increasing number of syllables) and
(2)I do not know where (increasing number of letters)

Etymology -
The word derives from the Greek rhopalos, a club that is thicker at one end.

Oxford English Dictionary -
Its first citation is from 1682:
"Of Ropalic or Gradual Verses…. A Poem of this nature is to be found in Ausonius beginning thus…. "
(a1682 Sir T. Browne Misc. Tracts vii. (1683) 125)

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