A rider, not a lever
A pedaller, in ordinary British English, is a person who pedals. The word almost always names a cyclist, though it can fit anyone working a machine with the feet. American spelling usually writes pedaler, with a single l. Some dictionaries add a second, less personal sense: a thing built to be pedaled, such as a desk-cycle or an ordinary bicycle spoken of as a machine rather than a ride. The extra l in the British form is spelling, not a separate word. English that doubles a final l before a suffix, as in travelling, labelled, or pedalling, does the same here.
The noun is young. It was not inherited from Old English and was not borrowed ready-made from French. It was assembled in English from pedal and the agent suffix -er.
An English coinage of the 1880s
The origin of the word pedaller is a straightforward derivation. Standard historical dictionaries date the first known use to 1881, in the cycling press of the high-wheel period. One major record cites the paper Wheeling. That decade is the right setting. Ordinary bicycles with a huge front wheel were already a public craze; the chain-driven safety bicycle that made riding ordinary was still a few years away. English needed a plain name for the person turning the cranks, beside older labels such as wheeler and the slightly later cyclist, formed from cycle plus -ist around 1882.
Whether the -er was added to the noun pedal or to the verb is hard to settle, and the evidence pulls both ways. Historical dictionaries list both etymons. The verb is recorded of organ playing by the mid-1860s, but of bicycles only toward the late 1880s, after the agent noun itself. A formation from the noun is therefore at least as likely: a pedaller as someone associated with pedals, on the same pattern as potter or miller. Either analysis is morphologically ordinary. What is striking is the date. The foot-lever had been in English for two and a half centuries; the person-word appears only when cycling made the lever a way of moving down the road.
From Latin foot to organ key
The stem is older than the agent noun. Pedal reached English in the 1610s as the name of a lever on an organ worked by the foot. The immediate source was French pédale, taken from Italian pedale, a treadle or pedal. Behind the Italian is Late Latin pedale, used of something belonging to the foot, the neuter of the adjective pedālis.
That adjective had two well-attested lives in Classical Latin, and modern dictionaries do not always put the same one in the etymology line. Pedālis could mean of or belonging to the foot. It could also mean a foot in length, width, or thickness: a beam a foot across, the apparent width of the sun. Both senses are genuine. The mechanical meaning that passed through Italian and French grew from the body part, not from the measuring-stick, even if some desk dictionaries still gloss the Latin with the measure.
The Latin formation is transparent: pēs, genitive pedis, foot, plus the adjectival suffix -ālis. Pēs is the Italic descendant of the Indo-European word for foot, reconstructed as *pṓds / *ped-. Germanic inherited the same root and, by the regular shift of p to f, produced English foot and German Fuß. Greek pous, Sanskrit pad-, and French pied are further relatives. English has borrowed the Latin stem many times in learned words: pedestrian, biped, impede, expedition, pedicure. Pedaller is mixed in a different way. Its last syllable is the native Germanic agent ending; only the stem is Latin, and that stem arrived through everyday French and Italian, not through a schoolroom coinage.
French later built a parallel agent, pédaleur, from the verb pédaler. Italian has pedalare for the action. Those are sibling formations, not the source of the English noun.
How the sense narrowed to cycling
Once the organ sense was in English, the noun widened. By the late eighteenth century it could name any machine part that takes power from the operator’s foot: looms, later sewing machines, then the bicycle crank. The verb followed: to work such a lever. Cycling then specialised the agent noun. A pedaller in current use is a rider, not an organist, even though the organist still pedals.
There is no lost medieval sense to recover. The interesting change is social rather than semantic. A technical name for a foot-lever became, through the Victorian bicycle boom, a name for a person. The word never displaced cyclist, which names the activity as membership in a sport or habit. Pedaller stays closer to the physical work: the person doing the job with the feet. That is why it still fits a recumbent rider, a unicyclist, or a tourist on a hired bike, without implying racing kit.
The American single-l spelling is the same word under a different house rule. It does not mark a different meaning.
The date that belongs to the rider
The Latin foot-word is ancient, and the organ pedal is early modern. The person called a pedaller is neither. Keep 1881: a Victorian cycling paper, a borrowed stem, and a native suffix, put together when wheeling turned a foot-lever into a way of travelling. The extra l in the British spelling is a small reminder that English built this noun at home.