pilus

This term is primarily used in microbiology and anatomy to describe hair-like projections. In a bacterial context, it refers to specialized protein tubes used for adhesion or conjugation, where genetic material is exchanged between cells. This technical usage is distinct from the general anatomical sense referring to a single hair.

Because the word is derived from Latin, it follows an irregular pluralization pattern. Instead of adding a standard English suffix, the plural form changes the ending to -i, which is common for biological and medical terminology of Latin origin.