Webster's 1913 Dictionary
BACTERIUM
Bac *te "ri *um, n.; pl. Bacteria. Etym: [NL. , fr. Gr. ,, a staff: cf. F. bactérie. ] (Biol.)
Defn: A microscopic vegetable organism, belonging to the class Algæ, usually in the form of a jointed rodlike filament, and found in putrefying organic infusions. Bacteria are destitute of chlorophyll, and are the smallest of microscopic organisms. They are very widely diffused in nature, and multiply with marvelous rapidity, both by fission and by spores. Certain species are active agents in fermentation, while others appear to be the cause of certain infectious diseases. See Bacillus.
New American Oxford Dictionary
bacterium
bac te ri um |bakˈti (ə )rēəm bækˈtɪriəm | ▶noun ( pl. bacteria |-ˈti (ə )rēə | ) a member of a large group of unicellular microorganisms that have cell walls but lack organelles and an organized nucleus, including some that can cause disease. Bacteria are widely distributed in soil, water, and air, and on or in the tissues of plants and animals. Formerly included in the plant kingdom, they are now classified separately (as prokaryotes ). They play a vital role in global ecology, as the chemical changes they bring about include those of organic decay and nitrogen fixation. Much modern biochemical knowledge has been gained from the study of bacteria because they grow easily and reproduce rapidly in laboratory cultures. DERIVATIVES bac te ri al |-ˈti (ə )rēəl |adjective ORIGIN mid 19th cent.: modern Latin, from Greek baktērion, diminutive of baktēria ‘staff, cane ’ (because the first ones to be discovered were rod-shaped ). Compare with bacillus . usage: See usage at bacteria .
Oxford Dictionary
bacterium
bacterium |bakˈtɪərɪəm | ▶noun ( pl. bacteria |-rɪə | ) a member of a large group of unicellular microorganisms which have cell walls but lack organelles and an organized nucleus, including some which can cause disease. Bacteria are widely distributed in soil, water, and air, and on or in the tissues of plants and animals. Formerly included in the plant kingdom, they are now classified separately (as prokaryotes ). They play a vital role in global ecology, as the chemical changes they bring about include those of organic decay and nitrogen fixation. Much modern biochemical knowledge has been gained from the study of bacteria, as they grow easily and reproduce rapidly in laboratory cultures. DERIVATIVES bacterial adjective, bacterially adverb ORIGIN mid 19th cent.: modern Latin, from Greek baktērion, diminutive of baktēria ‘staff, cane ’ (because the first ones to be discovered were rod-shaped ). Compare with bacillus . usage: Bacteria is the plural form (derived from Latin ) of bacterium. Like any other plural it should be used with the plural form of the verb: the bacteria causing salmonella are killed by thorough cooking, not the bacteria causing salmonella is killed by thorough cooking. However, the unfamiliarity of the form means that bacteria is sometimes mistakenly treated as a singular form, as in the example above.
Sanseido Wisdom Dictionary
bacterium
bac te ri um /bæktí ə riəm /名詞 bacteriaの単数形 .
The Wordsmith Dictionary