What does sill mean?
A sill is a horizontal ledge or structural base, most commonly the piece beneath a window and therefore also called a windowsill. Doors and other openings can have sills as well, and in general architectural description the word can refer to a lower threshold or boundary. In older, literary English, “sill” could also be used contemptuously for a person, a sense that helps explain the development of “silly” and “silliness.” Today the word is primarily practical and architectural, but it retains a slightly old-fashioned quality when it appears in formal descriptions of buildings. It should not be confused with the more general “ledge”: a sill is usually a particular base or frame, while a ledge may be any projecting shelf on a wall, cliff, or other surface.
A horizontal ledge or base, especially beneath a window or door; by extension, a threshold or lower boundary.
"The morning light fell across the stone sill."
The contemptuous sense for a person is now chiefly literary or old-fashioned.
To furnish an opening or structure with a sill.
"The opening was silled with a broad stone ledge."
This is a rare technical or literary verb.
Used for separate window sills, door sills, or other architectural ledges.
"The mason fitted new sills beneath the windows."
The word that names the ledge beneath a window also helps explain the origin of “silly”: foolishness was once associated with being beneath serious or sensible consideration.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does sill come from?
The word comes through Middle English sille, usually traced to an Old English word related to the base of a structure or building. Its development also connects with the sense of something or someone contemptible, from which words such as “silly” were formed. The modern architectural meaning refers to the lower horizontal member supporting or finishing an opening.
Related word forms
How sill is actually used
In modern usage, “sill” usually refers to the structural base of a window or door. The sense meaning a contemptuous person is uncommon and sounds deliberately archaic or dismissive.
Easily confused with sill
A sill is a specific structural base or horizontal frame, such as the one beneath a window, whereas a ledge is a broader shelf or projecting platform along a wall or rock face.