'bacillaceae' originates from New Latin, specifically the word 'Bacillaceae', where 'Bacillus' derived from Latin 'bacillum' meant 'little rod' and the suffix '-aceae' denoted a family (in botanical/zoological taxonomy).

'bacillaceae' developed from Latin 'bacillum' (diminutive of 'baculum', meaning 'rod' or 'stick'), through the genus name 'Bacillus' in modern scientific Latin, and later gained the family-forming suffix '-aceae' in Neo-Latin taxonomy to form 'Bacillaceae'.

Initially referring to the small rod-like shape ('little rod'), the term evolved in scientific usage to denote a taxonomic family of bacteria (the family Bacillaceae).