Origins
The English word 'teacher' is an agent noun formed from the verb 'teach' with the suffix '-er,' following a pattern of occupational naming that stretches back to Old English. The verb itself, Old English 'tǣcan,' descended from Proto-Germanic *taikijaną (to show, to point out), which in turn derives from Proto-Indo-European *deyḱ- (to show, to point). The teacher, at the deepest etymological level, is 'the one who points things out.'
The PIE root *deyḱ- generated an extraordinarily productive family of words across the daughter languages. In Latin, it became 'dīcere' (to say, to speak — originally 'to point out verbally'), the source of English 'dictate,' 'dictionary,' 'diction,' 'predict,' 'verdict,' 'indicate,' 'index,' 'judge' (from 'iūdex,' literally 'one who points out the law'), and 'condition.' In Greek, it produced 'deiknýnai' (to show, to demonstrate), the root of 'paradigm' (a pattern shown alongside), 'deictic' (pointing, demonstrative), and 'policy' (through 'apodeixis,' demonstration). In Sanskrit, 'diśáti' (he points, he shows) generated 'deśa' (region, literally 'what is pointed out') and 'adeśa' (instruction).
The Germanic branch took a different semantic path. Proto-Germanic *taikijaną kept the physical sense of 'showing' and 'indicating,' producing Old English 'tǣcan' (to show, to instruct) and the related noun *taikną (a sign, a mark), which became Old English 'tācn' and Modern English 'token.' German 'zeigen' (to show, to point) is the exact cognate of English 'teach,' though their meanings diverged: English 'teach' narrowed from 'show' to 'instruct,' while German 'zeigen' kept the original sense of physical pointing and showing. The Grimm's Law correspondence is regular: PIE *d became Germanic *t, and PIE *ḱ became Germanic *k (later /tʃ/ in English through palatalization).
Old English Period
The Old English agent noun 'tǣcere' is attested from the earliest period of written English. In Anglo-Saxon society, the tǣcere was not exclusively a schoolroom figure — the word applied to anyone who showed, instructed, or demonstrated, including preachers, master craftsmen, and wise counselors. The more specific sense of a professional employed to instruct the young emerged gradually during the Middle English period, solidifying as formal schooling became more widespread after the establishment of grammar schools and universities.
The spelling and pronunciation evolved considerably. Old English 'tǣcan' had the vowel /æː/, which by regular sound change became Middle English /ɛː/ and then Modern English /iː/ (the 'ea' of 'teach' following the Great Vowel Shift). The agent suffix '-ere' (Old English) became '-er' in Middle English, the standard form for occupational nouns that English has used continuously for over a thousand years — 'baker,' 'miller,' 'weaver,' 'singer,' and scores of others follow the same pattern.
English possesses a telling doublet in its vocabulary for instruction. The Germanic 'teach' carries connotations of practical, direct instruction — pointing out, showing how. The Latinate 'educate' (from Latin 'ēducāre,' to lead out, to rear) carries connotations of systematic, institutional formation. 'Instruct' (from Latin 'instruere,' to build into, to equip) implies structured, methodical training. A teacher teaches; an educator educates; an instructor instructs — but only the first word preserves the ancient metaphor of pointing, of physically directing attention to what matters.
Proto-Indo-European Roots
The cultural weight carried by the word 'teacher' varies enormously across societies, but the etymological core — the pointer, the shower, the one who makes visible what was hidden — remains a remarkably apt description of what good teaching actually does. The PIE speakers who coined *deyḱ- some six thousand years ago could not have anticipated that the simple act of pointing a finger would generate words for speech, law, justice, instruction, and demonstration across dozens of languages, but the semantic logic is sound: to point is the first act of communication, and the teacher is the professional pointer.