claustellī genitive singular of claustellum...
claustellīs dative/ablative plural of claustellum...
IPA(key): /klau̯sˈtel.lum/, [kläu̯sˈt̪ɛlːum] claustellum n (genitive claustellī); second declension keyhole c. 27 CE – 66 CE, Petronius, Satyricon 140:...