Ceil comes from Middle English celen ('to line the inner roof'), of uncertain origin; perhaps from Old French celer ('to conceal') from Latin celare ('to hide'), or influenced by Latin caelum ('heaven, ceiling'). The historical trail runs through celare in Latin. The history must be left partly open, preserving the uncertainty rather than forcing a single unsupported ancestry. Used as a verb, ceil now means "line or cover the inner roof of a room with plaster or boards", so the present definition can be read against the older forms and meanings. The same lexical family is also visible in derived forms such as ceiling and related forms such as ceiling. That uncertainty is part of the entry: the safest account is the attested form and the limited comparisons preserved with it.