Contact, and then almost everything else
In ordinary English, to touch something is to bring a hand, a finger, or another surface into contact with it. The verb also covers contact that nobody planned: a hem that meets the floor, two shoulders that meet in a crowd. Around that core sit many non-physical uses. A story can touch a listener. Someone may refuse to touch a subject, or barely touch a meal. To stay in touch is to keep communication going. The noun names the act, the tactile sense, a slight amount, a knack, and, in older technical speech, a test of metal. The origin of the word touch is a French borrowing that English then stretched in all of those directions.
How it entered English
English did not inherit this verb from Old English. Around 1300, Middle English writers were using touchen, also spelled tochen, for deliberate physical contact, often with the hand. The immediate source is Old French tochier, later toucher: to touch, hit, or knock, and also to mention or deal with a matter. Anglo-French forms such as tucher and tuchier travelled with the same cluster of senses.
The noun arrived in the same stretch of Middle English, as touche or toche. It came partly from the Old French noun toche or touche, which already meant a touching, a blow, an attack, or a test, and partly by turning the English verb into a noun. The earliest firm evidence for the noun falls before 1325; other dictionaries date both verb and noun to the fourteenth century. Either way, the path is a loan from French after the Norman period, not a native Germanic survival.
A native verb of contact did exist. Middle English still used rinen, from Old English hrīnan, meaning to touch or come into contact. Touch largely displaced it. A thin remnant survives as the rare modern form rine. The pattern is familiar: a French loan takes over the common meaning, and the older English word fades.
The Latin verb, and a split in the sources
Old French tochier is traced to a reconstructed Vulgar Latin verb, usually written toccare or toccāre, meaning to knock or strike, including the striking of a bell. That form is not recorded in Classical Latin. It is inferred from the Romance family. Spanish tocar, Italian toccare, and French toucher all point back to the same spoken Latin verb of knocking and then of contact.
What that Latin verb itself comes from is where the references disagree. Several major dictionaries treat toccare as probably imitative: a word shaped after the sound of a tap or knock. On that account there is no deeper Indo-European root to chase. The verb starts as a noise-word in spoken Latin and then spreads through Romance.
Other historical accounts take a Germanic route. They derive the same Vulgar Latin verb from Frankish tukkōn, a word of knocking, striking, or touching, itself from Proto-Germanic tukkōną, to tug, grab, or grasp, and ultimately from the Proto-Indo-European root dewk-, to pull, draw, or lead. On that reconstruction, English touch sits at a distance from native words such as tug, tow, and team, and is a doublet of tuck. German zucken, to jerk or flinch, and Dutch tokkelen, to strum or pluck, belong to the same Germanic group.
Romance languages really do share a knock-and-touch verb of this shape, and Germanic really does have a family of tug-and-grab verbs that look similar. The open question is whether spoken Latin coined the word from sound or took it from Frankish. The last step is uncertain. The step into English is not: French, then Middle English.
From a blow to a light contact
Old French already mixed force with contact. Tochier could mean to hit as well as to touch. The early English noun could mean a blow, a wound, or an injury as well as the making of contact. The later, gentler sense is a thinning of that older meaning: the lightest stroke is only a touch. By the mid-fourteenth century the verb also covered incidental or involuntary contact. By the late fourteenth it could mean to border on, to reach, or to attain, and to handle or have to do with a matter.
Figurative uses stacked onto the physical ones instead of replacing them. From the mid-fourteenth century, to touch someone could mean to affect the mind or feelings. From the late fourteenth, not to touch food or drink meant not to partake. Musicians touched strings, and later keys. In drawing and painting, a touch became a mark made with brush or pencil, and then a name for skill in making such marks.
From the sixteenth century, words could touch a person in the sense of sting or wound. From the seventeenth, money could be touched in the sense of received, sometimes by shady means; by the eighteenth, to touch someone for money was to borrow. Touched as a word for mentally unstable is recorded from the early eighteenth century.
The noun followed a technical track of its own. Goldsmiths tested gold and silver by rubbing them on a touchstone and comparing the streak with needles of known alloy. From that practice came the idea of a small quantity that leaves a mark, by the 1580s, and later the everyday sense of a slight amount, or a slight attack of illness. In or out of touch, meaning whether communication is maintained, is recorded from 1884. To lose one’s touch, meaning to lose a customary knack, appears in the twentieth century, probably from the musical and painterly sense. Soft touch, a person easily imposed on, is recorded from about 1940. Romance cognates keep some of the older knock: Italian toccare and Spanish tocar still cover striking a bell or playing an instrument as well as light contact.
What remains visible
The everyday English verb of contact is a French loan that replaced a native word. Behind French sits an unwritten Latin verb of knocking, shared with Spanish and Italian. Whether that Latin verb is a tap imitated in sound or a Germanic cousin of tug is still unsettled. What is not unsettled is the drift of the meaning: a word that could once name a blow settled, in English, on the lightest contact, and then on almost every kind of contact that stops short of a grasp. The displaced Old English verb hrīnan is the quiet proof that English already had a word for the same act, and chose another.