English
regular open
From regular + open; apparently a backformation from regular open set.
Proto-Indo-European *h₃reǵ- ‘move in a straight line’
Latin rēgula ‘rule’
Latin rēgulāris ‘continuing rules for guidance’
Anglo-Norman reguler
Middle English reguler
English regular
Proto-Indo-European *upo ‘up from under, over’
Proto-Germanic *upanaz ‘open’
Proto-West Germanic *opan
Old English open ‘open’
Middle English open
English open
Today it means
adj Being the interior of its closure.
Sources
Sources: Wiktionary, “regular open”. By Wiktionary contributors, CC BY-SA 4.0, via kaikki.org (dump of Oct 3 2026); text adapted and restructured. Language periods are conventional ranges, not dates for this word. License.
Etymograph / regular open