Q: Why do we say “roof of the mouth” rather than “ceiling”? A friend asked me this and I had no idea but I thought maybe you would.
A: The noun “roof” appeared in English hundreds of years earlier than “ceiling,” and its use for the upper part of the mouth was firmly established well before “ceiling” arrived in Middle English.
Interestingly, in Old English “roof” meant the upper interior surface of a room as well as the upper exterior surface of a building. Both senses were recorded in the 10th century.
The Oxford English Dictionary defines the inside sense of “roof” (hrof in Old English) as “the interior overhead surface of a room or other covered part of a house, building, etc.; the ceiling. Also: the upper internal surface of a cave or other structure.”
The earliest OED example is in a glossary of the mid-10th century in which lacunar (Latin for ceiling or paneled ceiling) is defined as hrof, hushefen (“house heaven”), or heofenhrof (“heaven’s roof”). From The Latin-Old English Glossary in MS Cotton Cleopatra AIII (1951), by William Garlington Stryker.
The dictionary’s next example is from The Homilies of the Anglo-Saxon Church, written around 990 by the Benedictine Abbot Ælfric of Eynsham:
“Se hrof eac swilce hæfde mislice heahnysse; on sumre stowe hine man mihte mid heafde geræcan, on sumre mid handa earfoðlice” (“The roof also was of various heights: in one place a man might reach it with his head, in another barely with his hand”).
The dictionary defines the outside sense of “roof” as “the external upper covering of a house or other building; the framing structure on top of a building supporting this. Also: a rooftop.”
The OED’s earliest citation (using the plural hrofum) is from an Old English gloss, or translation, inserted in the late 10th century between the lines of Latin in the Lindisfarne Gospels, dating from the early 8th century:
“þætte in eare sprecend gie woeron in cottum aboden bið on hrofum” (“what you have spoken in the ear [whispered] in bedchambers shall be proclaimed from rooftops,” Luke 12:3).
The OED defines the sense of “roof” you’re asking about as an extended or figurative use of “roof” for “the upper surface of the oral cavity; the palate.” The first citation is from an Old English gloss added in the 11th century to the margins of a 10th-century Latin grammar:
“goma uel hrof þæs muðes” (“palate or roof of the mouth”). From the Antwerp part of the Antwerp-London Glossaries. The manuscript, split into two, includes glosses from the margins of Excerptiones Prisciani (Excerpts From Priscian). Priscian was a Latin grammarian of the early 6th century.
As for “ceiling,” the OED says that when the noun first appeared in the late 14th century it referred to “the wooden lining of the roof or walls of a room: panelling; wainscoting.” Here’s the dictionary’s first citation for this now obsolete sense:
“Þe celynge with-inne was siluer plat & with red gold ful wel yguld” (“the ceiling within was silver plate and with red gold full well gilded”). From Sir Ferumbras (circa 1380), a medieval romance about a Saracen knight.
Today, “ceiling” means the upper lining of a room and “roof” usually means the upper covering of a building. And as we’ve said, for close to a thousand years “roof” has also meant the upper interior of the mouth.
But “roof” is still sometimes used in an another “inside” sense—as in the highest part of a cave, tunnel, mine or other underground space, and the underside of an overhanging ledge.
We’ll end with a modern example that the OED found in Postcards From the Ledge: Collected Mountaineering Writings of Greg Child (1998). In this passage, the Australian mountaineer encounters a storm of snow pellets after climbing around the roof of a ledge:
“In the afternoon, as Greg climbs around a small roof and launches up a groove, a cloud appears out of nowhere and spills a deluge of graupel.”
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