di·a·to·ma·ce·ae I. \ˌdīəd.əˈmāsēˌē, (ˌ)dīˌad.ə-\ Etymology: New Latin, from Diatoma, type genus + -aceae synonym of bacillariaceae II. noun plural Usage: capitalized Etymology: New Latin, from Diatoma, type genus + -aceae : a family of rectangular diatoms