Origins
The word 'tide' is one of the most striking examples of semantic narrowing in English.βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ In Old English, 'tΔ«d' meant simply 'time, period, season, hour' β a general temporal word with no connection to the sea. It descends from Proto-Germanic *tΔ«diz (time, period), from PIE *dehβy-ti- (a division), from the root *dehβy- (to divide, to cut up). Time, in the Indo-European conception, was something divided into portions β cut up into segments.
The Germanic cognates preserve the original 'time' meaning without exception: German 'Zeit' (time), Dutch 'tijd' (time), Swedish 'tid' (time), Norwegian 'tid' (time), Danish 'tid' (time), Old Norse 'tΓΓ°' (time, season, hour of prayer). English alone shifted the word from 'time' to the 'periodic rise and fall of the sea.' This shift occurred gradually during the Middle English period, as the metaphor 'the tide of the sea' (i.e., 'the time/season of the sea, its appointed rhythm') was used so frequently that 'tide' alone came to mean the phenomenon.
The older 'time' sense survives in fossilized compounds and archaic forms. 'Eventide' (evening-time), 'Christmastide' (the Christmas season), 'Whitsuntide' (the Whitsun season), 'noontide' (noon-time), and 'Shrovetide' (the season before Lent) all preserve 'tide' = 'time.' The word 'tidings' (news, things that happen at a particular time) and the verb 'betide' (to happen to, as in 'woe betide') also carry the original temporal sense. Even 'tidy' originally meant 'timely, seasonable' before shifting to 'orderly, neat.'
Old English Period
The reason English alone made this semantic shift is geographical. The Anglo-Saxons settled an island nation where tidal rhythms governed daily life β fishing, navigation, trade, and coastal defense all depended on knowing the tide's schedule. The twice-daily rise and fall of the sea was the most conspicuous periodic phenomenon in coastal existence, more reliable than weather, more visible than the moon's phases. Calling it 'the time' was natural, and eventually 'the time' became the thing itself.
The PIE root *dehβy- (to divide) also produced Greek 'daiesthai' (to divide), 'dΔmos' (a division of people β 'democracy'), and possibly 'daimon' (a divider of fate, a spirit). The connection between dividing and time-keeping reflects a deep Indo-European insight: time is not experienced as a continuous flow but as a sequence of divisions β days, seasons, tides. To mark time is to cut the continuum into portions.
In modern English, 'tide' has been re-extended metaphorically: 'a tide of public opinion,' 'the rising tide of nationalism,' 'the tide has turned.' These expressions preserve the sense of a large, slow, periodic, and somewhat inexorable movement β qualities the metaphor inherits from the sea.