'unsplit' originates from English, formed by the negative prefix 'un-' + the verb 'split', where 'un-' meant 'not' and 'split' comes from Old English/Germanic roots related to dividing or cleaving.

'split' comes from earlier Germanic and Old English forms (compare Old English 'splītan' and Middle English 'splitten'); 'unsplit' is a Modern English formation that joins the prefix 'un-' to that base to indicate the negation or reversal.

Initially, the components meant 'not' + 'to divide/cleave'; over time 'unsplit' has been used both adjectivally ('not split') and verbally ('to make unsplit' or 'to reverse a split').