Origins
The word 'rain' descends from Old English 'regn' (rain), from Proto-Germanic *regna- (rain), from PIE *hβreΗ΅- (to moisten, to wet).βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ It is one of the most ancient and semantically stable words in the English language β the concept it denotes has required no metaphorical extension, no narrowing, no broadening. Rain has always meant rain.
The Proto-Germanic form *regna- is reflected with remarkable consistency across the family: German 'Regen,' Dutch 'regen,' Old Norse 'regn,' Swedish 'regn,' Danish 'regn,' Norwegian 'regn,' and Gothic 'rign.' The phonological development from Old English 'regn' to Modern English 'rain' involved the vocalization of the velar consonant 'g' β the hard 'g' sound weakened to a glide and was eventually absorbed into the vowel, lengthening it into a diphthong. This same process affected many Old English words: 'dΓ¦g' became 'day,' 'weg' became 'way,' 'mΓ¦gen' became 'main.'
The PIE root *hβreΗ΅- (to moisten) is also the likely ancestor of Latin 'rigΔre' (to wet, to water, to irrigate), which entered English through 'irrigate' (from Latin 'irrigΔre,' in- + rigΔre, to water thoroughly). If this connection holds β and most etymologists accept it β then 'rain' and 'irrigate' are cousins: the Germanic branch preserved the noun (the water that falls), while the Italic branch preserved the verb (the act of wetting).
Germanic Development
Compound words built on 'rain' reveal how the Germanic languages construct meaning from native elements. 'Rainbow' is Old English 'regnboga' β literally 'rain-bow,' an arc made visible by rain. Every Germanic language independently assembled the same compound: German 'Regenbogen,' Dutch 'regenboog,' Swedish 'regnbΓ₯ge,' Danish 'regnbue.' This parallel construction suggests the compound may predate the breakup of Proto-Germanic, or that the metaphor was so natural it arose independently in each branch.
Old English distinguished between 'regn' (rain as a substance, the phenomenon) and 'scΕ«r' (a shower, a brief burst of rain β modern English 'shower'). This distinction between the general concept and a specific instance has been preserved: 'rain' is the broad term, 'shower' is a lighter, shorter event. The word 'storm' was reserved for violent weather of all kinds, not rain specifically.
In figurative usage, 'rain' has been extended to mean any abundant downpour: a rain of arrows, a rain of blows, a rain of praise. The verb 'to rain' (Old English 'regnian') developed the impersonal construction 'it rains' β one of those rare English sentences where 'it' refers to nothing at all. This impersonal weather construction is ancient, found across Indo-European languages: Latin 'pluit' (it rains), German 'es regnet' (it rains), French 'il pleut' (it rains). No one performs the action; rain simply happens.