i think that is wrong. siparah is actually a contraction of the word sīpārah which means thirtieth part. that is what lexicons tell us. so also in urdu, a siparah is ONE PART of the thirty parts in the qur'an. the usage of siparah/sīpārah for a single juz'u/part is correct as far as my knowledge permits even though breaking down words to stand under may not work always.
Hey....this is cool. Very interesting! Things like this really make me want to learn another language........... Ok..............so the same word in the naat that goes 'Kaaliyaan zulfaan waala': 'Parh Kay Tu Weykh Jeyra Marzi Sipaara, Qassam Khudaa Dii Maynoon etc etc'. Is this also technically incorrect then? hmmm...
i don't know much farsi at all so correct this if i'm wrong: the farsi word si means 30 paara means part so the Qur'an is knows as sipaara. so it would actually be incorrect to say, as is the norm, that i have read 13 sipaare to mean i have read 13 parts. you would say 13 paare.