Origins
The verb 'grow' is one of the most elemental words in English, touching on biology, agriculture, personal development, and economic expansion. Its etymology roots it in the most basic observation of the natural world: the sight of green things emerging from the earth. The word descends from Old English 'grōwan,' a strong verb meaning 'to grow, to flourish, to germinate,' from Proto-Germanic *grōaną, from PIE *gʰreh₁-, meaning 'to grow' or 'to become green.'
The PIE root *gʰreh₁- is the source of a compact but significant family of English words, all connected by the theme of verdant life. 'Green' comes from Old English 'grēne,' from Proto-Germanic *grōniz, an adjective formed from the same root — literally 'growing, verdant.' 'Grass' descends from Old English 'græs,' from Proto-Germanic *grasą, the stuff that grows. 'Graze' (to feed on grass) is derived from 'grass.' All of these words — grow, green, grass, graze — descend from a single prehistoric syllable that captured the sight of vegetation coming to life.
The strong verb conjugation of 'grow' — grow/grew/grown — belongs to the seventh class of Germanic strong verbs, characterized by reduplication in Gothic (Gothic 'grōan') and a distinctive ablaut pattern in other Germanic languages. The vowel alternation between 'grow' /oʊ/, 'grew' /uː/, and 'grown' /oʊn/ is highly irregular by modern standards and has been preserved by the word's high frequency of use. Less common strong verbs have tended to regularize over time (compare 'mow/mowed/mown,' where 'mowed' as a past participle is increasingly common), but 'grew' shows no sign of giving way to a hypothetical 'growed.'
Word Formation
The compound 'grown-up' as a noun meaning 'an adult' dates from the early nineteenth century and encapsulates the identification of maturity with completed growth. 'Outgrow' (to grow beyond something) is attested from the sixteenth century. 'Overgrown' (grown excessively, covered in wild growth) is from the fourteenth century. Each compound preserves the core idea of natural, organic increase while specifying its direction or excess.
The phonological history of 'grow' shows the characteristic development of Old English /oː/ through the Great Vowel Shift. The Old English 'grōwan' had a long /oː/ vowel, which in Middle English remained as /oː/ and then, during the Great Vowel Shift, raised and diphthongized to the modern /oʊ/. The past tense 'grew' reflects a different vowel grade: Old English 'grēow,' with a diphthong that simplified to Middle English /ɛw/ and then raised to modern /uː/.
In the broader history of ideas, the metaphor encoded in 'grow' — that development is organic, that change is natural, that progress is like a plant reaching toward the sun — has been one of the most influential in Western thought. From Aristotle's concept of natural potential (dynamis) to Darwin's theory of evolution to the modern language of personal growth and self-actualization, the idea that living things unfold from within toward their fullest expression owes much to the simple observation that green things spring from the earth — the observation that gave the Proto-Indo-Europeans their word *gʰreh₁- and, through thousands of years of change, gave English the verb 'grow.'