(s)kel-
“to cover, to conceal, to shelter”cover/shelter
PIE root meaning to cover, conceal, or shelter, with an s-mobile prefix. Yields descendants related to hiding, shielding, and protective enclosures.
Discussion
*(s)kel- is a Proto-Indo-European root meaning "to cover," "to conceal," or "to shelter," featuring an s-mobile prefix—an optional initial *s- that appears in some branches but not others.
Without the s-mobile, the root yields Latin cēlāre ("to hide, to conceal"), giving English "conceal," "cell," and "clandestine." Greek kalýptein ("to cover") produces "apocalypse" (literally "uncovering") and "eucalyptus" ("well-covered," referring to the bud cap). Old Irish celid ("to conceal") also reflects the plain root.
With the s-mobile prefix, Germanic *skel- gives Old English scyll ("shell"), English "shell," "shield," "shelter," "skill" (originally "to separate, to distinguish"), and "skull." The s-mobile creates an apparent doublet in English: "conceal" (Latin, without s-) vs. "shell/shelter" (Germanic, with s-).
The semantic core involves creating a barrier between interior and exterior—covering, hiding, enclosing, protecting. This extends from physical sheltering (shells, shields, shelters) to abstract concealment (secrets, hiding). The root demonstrates how a single PIE concept of covering branched into both protective and deceptive meanings in the daughter languages.
Notes
Source of Latin "cēlāre" (to hide), English "shell", "shelter". S-mobile variant.