| ptarmigan | (noun) large Arctic and subarctic grouse with feathered feet and usually white winter plumage | - |
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| pteridologist | (noun) an expert in the study of ferns | - |
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| pteridology | (noun) the branch of botany that studies ferns | - |
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| pteridophyte | (noun) plants having vascular tissue and reproducing by spores | Synonyms: nonflowering plant |
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| pteridosperm | (noun) an extinct seed-producing fernlike plant of the order Cycadofilicales (or group Pteridospermae) | Synonyms: seed fern |
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| pterion | (noun) the craniometric point in the region of the sphenoid fontanelle | - |
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| pterodactyl | (noun) extinct flying reptile | - |
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| pteropogon | (noun) southern Australian plant having feathery hairs surrounding the fruit | Synonyms: Pteropogon humboltianum |
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| pterosaur | (noun) an extinct reptile of the Jurassic and Cretaceous having a bird-like beak and membranous wings supported by the very long fourth digit of each forelimb | Synonyms: flying reptile |
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| pterygium | (noun) either of two thickened triangular layers of conjunctiva extending from the nasal edge of the eye to the cornea; it arises from irritation of the pinguecula | - |
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| ptomain | (noun) any of various amines (such as putrescine or cadaverine) formed by the action of putrefactive bacteria | Synonyms: ptomaine |
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| ptomaine | (noun) a term for food poisoning that is no longer in scientific use; food poisoning was once thought to be caused by ingesting ptomaines | Synonyms: ptomaine poisoning |
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| (noun) any of various amines (such as putrescine or cadaverine) formed by the action of putrefactive bacteria | Synonyms: ptomain |
| ptosis | (noun) drooping of the upper eyelid caused by muscle paralysis and weakness | - |
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| ptyalin | (noun) an amylase secreted in saliva | - |
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| ptyalism | (noun) excessive flow of saliva | - |
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| ptyalith | (noun) calculus in a salivary gland | - |
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