did

The word 'did' — past tense of 'do' — descends from Old English 'dyde,' one of the most irregular pa‍​‍​‌​‌​‍​‌​‍​‍​‍​‌​‌​‍​‌​‍​‍​‍​‍​‍​‌​‍​‍​‍​‌​‍​‍​‌​‌​‌​‌​‍​‍​‌st tense forms in the language (the vowel change from 'dōn' to 'dyde' reflects an ancient reduplication pattern). It comes from Proto-Germanic *dōną (to do, to make), from PIE *dʰeh₁- (to put, to place, to do, to make).

The PIE root *dʰeh₁- is one of the most important verb roots in the entire family, producing fundamental words in every branch. Sanskrit 'dádhāti' (he puts, he places) preserves the reduplicated form. Greek 'títhēmi' (τίθημι, I put, I place) gave English 'thesis' (a proposition — something placed down), 'theme' (something set down), 'thesaurus' (a storehouse — a place where things are put), and 'apothecary' (one who puts things away — a storekeeper). Latin 'facere' (to do, to make), while showing a different initial consonant, is connected through a variant of the same root and produced 'fact' (a thing done), 'factory' (a place where things are made), 'fashion' (a way of doing), 'feat' (a thing done), 'effect' (a thing done out of), 'affair' (a thing to do — ad + facere), and 'office' (a doing of work — opus + facere).

Within English, *dʰeh₁- produced 'do,' 'did,' 'done,' 'deed' (a thing done), 'doom' (originally a judgment — something placed, a decree), and 'deem' (to judge, to place a decision). The '-dom' suffix in 'kingdom,' 'freedom,' 'wisdom' is from the same root — a domain is a sphere of judgment or authority.

The most remarkable feature of English 'did' is its role in do-support — the uniquely English requirement that questions and negatives use a form of 'do' as an auxiliary. Where German asks 'Sprichst du Deutsch?' (speak you German?) and French asks 'Parlez-vous francais?' (speak you French?), English requires 'Do you speak English?' Where German negates with 'Ich spreche nicht' (I speak not), English requires 'I do not speak.' This obligatory do-support developed gradually during the fifteenth through seventeenth centuries and is found in no other Germanic or major European language.

The origins of do-support remain one of the unsolved problems of English historical linguistics. It may have been influenced by Celtic substrate languages (Welsh and Cornish use a similar periphrastic construction), or it may have developed from the emphatic use of 'do' ('I DID see it') being generalized to questions and negatives. Whatever the cause, it fundamentally restructured English syntax and made 'did' one of the most frequently used words in the language — not because speakers do many things, but because the grammar demands it.