noun ·Rare ·Advanced level

Definitions

Noun

1. 1
   A bacterium that is considerably smaller than typical bacterial cells and is 0.2 to 0.3 micrometers (200-300 nm) in diameter.

Etymology

From ultra- + micro- + bacterium.

Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.