A small choice piece
In American English a tidbit is a small, especially appealing piece of food, or, just as often, a small, especially appealing piece of news. The two senses sit side by side: chocolate from a box, a scrap of gossip from a memoir. British English has long preferred the rhyming spelling titbit for the same pair of meanings. Neither form was borrowed from French or Latin. Both are English compounds whose second half is clear and whose first half has never been fully settled.
English from the start
The origin of the word tidbit is native and fairly late. The earliest citation usually given is from 1639, in John Smyth of Nibley's account of speech in the Hundred of Berkeley, Gloucestershire. He explains a tyd bit as a special morsel kept back to eat last. Two years later, in 1641, John Dawson's English version of a Latin treatise by Jeremias Drexel uses tit bits for choice scraps a servant might hope to take from a master's dishes. American dictionaries typically date first use around 1640. The spelling already wobbles: tyd bit, tid-bit, tit bit. That wobble is the whole problem of the first element.
The second element is not in doubt. Bit here is the old word for a morsel, a piece bitten off. It goes back to Old English bite, the act of biting, and bita, a piece bitten off, from a Germanic family that also yields German Bissen and Dutch bete, and further back to a Proto-Indo-European root reconstructed as *bheid-, to split. By the seventeenth century bit already meant a small amount of food. The compound names a particular kind of small bite. It was formed inside English, not imported.
The unsettled first half
Most historical dictionaries treat that first half as a dialect adjective tid, also spelled tyd or tidd. In Midlands records it could mean fond, attached, or careful of something; of a child, tender, nice, or fanciful. In Gloucestershire, Smyth himself glosses tyd as wanton, and a later county glossary gives tid as playful or frolicsome. Eighteenth-century lexicographers, starting with Nathan Bailey in 1727, listed tid as nice or delicate, largely because they found it sitting inside tid-bit. Samuel Johnson followed and guessed a link to Old English tídre or tyddre, words that meant weak or frail. That Old English pair cannot yield the later adjective, and the connection is now rejected.
The usual story, then, is that a tid bit was a tender, choice, or dainty bite. Oxford's learner materials still put it that way, calling dialect tid tender and of unknown origin. The American Heritage Dictionary is more cautious: perhaps an obsolete dialectal tid meaning tender, plus bit.
The caution is justified. Merriam-Webster notes that printed evidence for the dialect adjective and for the compound arrive at roughly the same moment in the mid-1600s. If they are twins rather than parent and child, tid may have been read back out of the compound rather than fed into it. Bailey's 1727 gloss looks like that kind of back-formation: an adjective generalized to explain a phrase already in use.
A rival account looks to a different first element: tit, the Middle English word for a small creature or object, the same tit that sits inside titmouse. That would make the compound a small bit of a small thing, which fits the sense neatly. The difficulty is chronological. The earliest spellings are tyd and tid, not tit. Tit bit appears in 1641, only two years after Smyth, so the rival is not late, but it is not first. Oxford thinks the later British titbit spelling is probably a rhyme adjustment: speakers reshaped tid to tit so that it would echo bit. A weaker suggestion is influence from tit and tittle, both used for tiny things.
A third, still less favored line appears in some American college dictionaries: tide in the old sense of a feast day, plus bit, as if the word named festival food. Old English tīd did mean a season, a canonical hour, a feast day, and that lineage is the ancestor of modern tide and of German Zeit. It is a real English word. The 1639 Gloucestershire evidence, however, points to tyd as a local adjective meaning wanton, not to the feast-day noun. The tide etymology does not match the earliest gloss.
What can be said with confidence is morphological, not ancestral. The word is an English compound of two native pieces. The first is either a poorly documented dialect adjective of unknown deeper origin, or a reshaping of tit, or, least likely, a clipping of tide. The second is bit, the bitten morsel, whose Germanic relatives are easy to name. The compound itself has no true cognates abroad; other languages simply translate the idea as a tasty scrap.
From reserved morsel to scrap of news
The food sense is the original one: a delicacy, a reserved last mouthful, a tasty scrap. By 1650 the word was already used of people and things likened to such a morsel. A London weekly associated with John Milton, Mercurius Politicus, could sneer at a political prize as if it were a choice bite of young Tarquin. Eighteenth- and nineteenth-century writers on both sides of the Atlantic kept both spellings for that figurative use.
The information sense is later and sharper. Oxford's first clear example is from 1809, in the Anti-Jacobin Review, where a tit bit of domestic scandal is a small, particularly interesting item of gossip. From there the modern pair of meanings is in place. American English kept tidbit as the usual form; British English settled on titbit. The American spelling is, ironically, closer to the 1639 tyd bit. The British spelling was reinforced, from 1881 to 1984, by Tit-Bits, a mass-circulation weekly of easy human-interest scraps that helped invent popular journalism. A newspaper named for the gossip sense will tend to lock in its own spelling.
The two senses never really split. A choice bite of food and a choice bite of news are the same metaphor.
Saved for last
The most concrete fact in the record is still Smyth's 1639 gloss. In one West Country hundred, a tyd bit was not any small piece. It was the morsel you saved for last. That reserved-last-bite meaning is the seed of both later uses: the chocolate you keep back, and the scrap of news you hold until the end of the story. The first half of the compound remains unsettled. The second half, the bite, has been clear for a thousand years.