This is the 760th most frequent Serbian word.
костолца
"Костолца" refers to something or someone related to the town of Kostolac in Serbia.
Here, 'Костолaц' is a proper noun referring to the name of a town.
Јуче сам посетио град Костолaц.
Yesterday I visited the town Kostolac.
In this sentence, ‘костолца’ refers metaphorically to a material property, resembling ivory.
Та статуа је направљена од костолца.
That statue is made of ivory.
Here, 'Костолцa' again refers to the town and indicates its geographic relationship to a nearby feature.