Origins
The word 'first' conceals one of the most counterintuitive facts in English etymology: it has nothing to do with the number one. While 'second' derives from Latin 'secundus' (following), 'third' from Old English 'þridda' (related to 'three'), and 'fourth' through 'tenth' all derive transparently from their cardinal numbers, 'first' stands apart. It is a superlative form meaning 'most forward' or 'most before.'
Old English had two forms: 'fyrst' and 'fyrest,' both functioning as the superlative of 'fore' (before, in front). The Proto-Germanic ancestor was *furistaz, built on the root *fur- (before, forward) with the superlative suffix *-istaz. This root descended from PIE *per-, one of the most versatile roots in Indo-European, meaning 'forward,' 'through,' or 'before.'
The PIE root *per- generated an astonishing range of English words through various channels. Through Germanic: 'for,' 'fore,' 'before,' 'forth,' 'forth,' 'further,' 'far,' 'former,' and 'first' itself. Through Latin (where *per- became 'pre-,' 'pro-,' and 'pri-'): 'primary,' 'prime,' 'prince,' 'prior,' 'primitive,' 'pristine,' 'premier,' 'privilege,' 'private,' 'problem,' 'provide,' 'produce,' and many more. Through Greek (where *per- became 'pro-,' 'proto-,' and 'para-'): 'protein,' 'prototype,' 'proton,' 'prophet,' and 'paradise.'
Proto-Indo-European Roots
The Germanic cognates of 'first' are illuminating. German 'Fürst' means 'prince' or 'sovereign' — the same Proto-Germanic superlative *furistaz, but with the meaning 'the foremost person' rather than 'the earliest in sequence.' This political sense reveals that in early Germanic society, being first was not merely a matter of order but of authority: the first person was the leader, the chief, the prince. Dutch 'eerst' (first) and the Scandinavian forms (Danish 'først,' Swedish 'först') preserved the ordinal meaning like English.
Latin 'primus' (first) descends from the same PIE root *per- through a different derivation: *pr̥h₃-mo- (foremost). This gave English 'primary,' 'prime,' 'primitive,' 'premier,' and 'prince' (from Latin 'princeps,' literally 'first-taker' from 'primus' + 'capere'). Greek 'protos' (first), from PIE *pro- (a variant of *per-), gave English 'protein,' 'protocol,' 'proton,' and 'prototype.' All these words — 'first,' 'primary,' 'prime,' 'proto-' — are ultimately cousins, all meaning 'the one in front.'
The absence of a connection between 'first' and 'one' is actually the norm in Indo-European languages, not the exception. Latin 'primus' is not related to 'unus' (one). Greek 'protos' is not related to 'heis' (one). The concept 'first' was universally expressed not as 'the one-th' but as 'the most-before' — a superlative of position rather than a derivative of number.
Old English Period
In Old English, the word that did connect 'one' and 'first' was 'ǣrest' (earliest), a superlative of 'ǣr' (before, early), which survives in Modern English 'ere' and 'early.' But 'fyrst' won the competition, perhaps because its connection to 'fore' (in front, visible, spatial) was more vivid than 'ǣrest's' connection to temporal priority.
The word's modern uses span from the literal (first place, first floor, first edition) to the figurative (first-rate, first-class, first and foremost). The phrase 'first and foremost' is etymologically redundant — both words derive from the same Proto-Germanic root *fur-, making it literally 'most-before and most-before.' But redundancy in emphasis is a feature of English rhetoric, not a bug.