On the Origin of -s- in Spanish hasta

Extract

One of the conundrums of the historical phonology of Spanish is the seemingly intrusive -s- in the word hasta ‘until.’ Its putative etymon, the Arabic ḥattā ‘up to, until, as far as, even, in order to’ does not have this -s- and, as far as is known, has never had it. The most recent serious discussion of and accounting for this -s- that I am aware of is that presented by Malkiel (1979) in which, dismissing previous lexical and phonological attempts as inadequate, he suggests that hasta (earlier fasta) resulted from a contamination of its predecessor fata, coming unambiguously from ḥattā, with a Romance form fascas ‘nearly, almost,’ derived in part from Latin usque ‘until.’ Both fata and fascas then went out of use, and fasta (> hasta) alone remains. In spite of the wealth of documentation adduced by Malkiel, his evidence adds up to this: before roughly 1300, there was a -word fata ‘until’ and a word fascas ‘almost’; after 1300 both fell out of use, and there was a new word fasta ‘until.’ The rest is speculation.