bac·il·la·ri·a·ce·ae \ˌbasə̇ˌlerēˈāsēˌē\noun plural Usage: capitalized Etymology: New Latin, from Bacillaria, type genus (from Medieval Latin bacillus small rod + New Latin -aria) + -aceae — more at bacillus in some especially former classifications: a family equivalent to Bacillariophyceae • bac·il·la·ri·a·ceous\| ̷ ̷ ̷ ̷| ̷ ̷ ̷ ̷|āshəs\adjective