Four
Old English fēower, of Germanic origin; related to Dutch and German vier, from an Indo-European root shared by Latin quattuor and Greek tessares .
wiktionary
From Middle English four, from Old English fēower, from Proto-West Germanic *feuwar, from Proto-Germanic *fedwōr, from previous pre-Grimm *petwṓr, from Proto-Indo-European *kʷetwṓr, the neuter form of *kʷetwóres. Doublet of cuatro and quatre.
Cognates include West Frisian fjouwer, Dutch and German vier, Norwegian Bokmål and Danish fire, Swedish fyra, Gothic 𐍆𐌹𐌳𐍅𐍉𐍂( fidwōr) and, more distantly, Latin quattuor (whence Spanish cuatro, French quatre), Ancient Greek τέσσαρες(téssares), Irish ceathair, Armenian չորս(čʿors), Lithuanian keturi, Albanian katër, Sanskrit चतुर्(catur).
etymonline
four (adj., n.)
"1 more than three, twice two; the number which is one more than three; a symbol representing this number;" Old English feower "four; four times," from Proto-Germanic *fedwores (source also of Old Saxon fiuwar, Old Frisian fiower, fiuwer, Frankish *fitter-, Dutch vier, Old High German fior, German vier, Old Norse fjorir, Danish fire, Swedish fyra, Gothic fidwor "four"), from PIE root *kwetwer- "four." The phonetic evolution of the Germanic forms has not been fully explained; Watkins explains the -f- as being from the following number (Modern English five).
To be on all fours is from 1719; earlier on all four (14c.). Four-letter word as a euphemism for one of the short words generally regarded as offensive or objectionable is attested from 1923; four-letter man is recorded from 1920 (apparently as a euphemism for a shit). Compare Latin homo trium litterarum, literally "three-letter man," a euphemism for fur "a thief." A four-in-hand (1793) was a carriage drawn by four horses driven by one person; in the sense of "loosely tied necktie" it is attested from 1892. To study The History of the Four Kings (1760, compare French Livres des Quatre Rois) contains an old euphemistic slang phrase for "a pack of cards," from the time when card-playing was considered a wicked pastime for students. Slang 4-1-1 "essential information" (by 1993) is from the telephone number called to get customer information. The four-color problem so called from 1879. The four-minute mile was attained 1954.
