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Related to ostium: Ostium primum, Ostium secundum


n. pl. os·ti·a (-tē-ə)
1. A small opening or orifice, as in a body organ or passage.
2. Any of the small openings or pores in a sponge, through which water is drawn in.

[Latin ōstium, door, opening, from ōs, mouth; see ōs- in Indo-European roots.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


n, pl -tia (-tɪə)
1. (Zoology) any of the pores in sponges through which water enters the body
2. (Zoology) any of the openings in the heart of an arthropod through which blood enters
3. (Biology) any similar opening
[C17: from Latin: door, entrance]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014


(ˈɒs ti əm)

n., pl. -ti•a (-ti ə)
a small opening or orifice of the body.
[1655–65; < Latin ōstium entrance, river mouth]
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
References in periodicals archive ?
The term maxillo-ostio-choanal polyp was deemed appropriate in cases where it originates in the maxillary sinus ostium mucosa.
A single PV potential closely following or fused with an atrial potential in the ostium of the PVs is the most commonly observed pattern during sinus rhythm (SR) [7, 8].
The presence of RCMs, osteomeatal complex obstruction (OMCO), an accessory ostium, and abnormalities of the middle turbinate (AMT) were evaluated independently for the right and left sides.
An unusual medial ostium of a concha bullosa of the middle turbinate.
The aim of the present study is to assess the normal anatomy and variations of SA nodal artery by studying the number, origin, course, length and distance of its origin from the ostium of parent artery.
The distance of an individual ostium from the base of cusps of aortic valve by using Vernier caliper (Figure 2).
Other variables have been evaluated by computed tomography, such as ostium of the bronchial arteries in the aorta [23], the vertebral levels origin [14, 15, 18, 24], path through the posterior mediastinum [18], and diameter [14, 19, 25, 26].
In this case, the aneurysm extended into the coronary artery ostium. Coronary artery aneurysm, in contrast, is defined as coronary artery dilatation which exceeds the diameter of the largest normal coronary artery by 1.5 times.
According to the Neri's definition of coronary malperfusion in aortic dissection,[sup][2] we differentiated among three types of lesions based upon operative findings: type A ( n = 23), ostial dissection is defined as a disruption of the inner layer limited to the area of the coronary ostium without disrupting coronary vessel; type B ( n = 8), dissection with a coronary false channel; and type C ( n = 5), circumferential detachment with an inner cylinder intussusception.
DIAGNOSIS: Arm-lead reversal; normal sinus right atrial enlargement and right ventricular enlargement suggesting an ostium secundum atrial septal defect; acute inferior myocardial infarction.
Bony ostium was enlarged to an extent of approximately 1x1.5cm, bone overlying the upper part of nasolacrimal duct was also removed.
The above abnormality was accompanied by an ostium secundum-type atrial septal defect.