Here's how you pronounce it:
Parum:
* Par is pronounced like "par" in "park."
* um is pronounced like "um" in "hum."
Unus:
* U is pronounced like "u" in "flute."
* nus is pronounced like "nus" in "nucleus."
Therefore, the full pronunciation of "parum unus" is: PAR-um OO-nus.