as·​cus ˈa-skəs How to pronounce ascus (audio)
plural asci ˈa-ˌskī How to pronounce ascus (audio) -ˌskē How to pronounce ascus (audio)
: the membranous oval or tubular spore case of an ascomycete

Word History


New Latin, from Greek askos wineskin, bladder

First Known Use

1828, in the meaning defined above

Time Traveler
The first known use of ascus was in 1828

Dictionary Entries Near ascus

Cite this Entry

“Ascus.” Dictionary, Merriam-Webster, Accessed 20 Jul. 2024.

Medical Definition


1 of 2 noun
as·​cus ˈas-kəs How to pronounce ascus (audio)
plural asci ˈas-ˌ(k)ī How to pronounce ascus (audio) -ˌkē How to pronounce ascus (audio)
: the membranous oval or tubular sporangium of an ascomycete


2 of 2 abbreviation
variants also AS-CUS
atypical squamous cells of undetermined significance

Note: ASCUS is a diagnosis used in cytology to describe the presence of abnormal squamous cells in a Pap smear test. Upon staining, these cells exhibit an atypical appearance (as enlarged nuclei or irregular shape) that cannot definitively be classified as benign or precancerous.

Many physicians believe that combining the Pap test with direct virus testing may prove particularly useful when a pap test comes back with its most common indeterminate result, called ASCUS—atypical squamous cells of undetermined significance.Jerome Groopman, The New Yorker
Currently, there is no consensus on what to do with ASCUS patients, only 5% to 10% of whom actually have precancerous cells.Rita Rubin, USA Today

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