This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
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adj. Of or pertaining to the protists

Of or pertaining to the Protista.

n. A member of the Protista; any unicellular organism not definitely regarded as a plant or an animal.

n. free-living or colonial organisms with diverse nutritional and reproductive modes

"The digestive tracts of herbivorous fishes may contain protistan and bacterial endosymbionts that aid in the digestion of the plant material."

microorganism