10th cent. From Latin ad sic "(towards) so." For the etymology of Latin ad, see a; for the etymology of sic, see sí.Also possible is that the word came from Vulgar Latin ac sic "so," frequently used by the author of the Vulgar Latin text Peregrinatio (4th cent.). The problem is medial -cs- in ac sic would have palatalized in Spanish, which it did not here. Latin ac is short for atque "and," "as." From ad "toward" and -que "and." For their etymologies, see a and -que respectively.
Asturian (Somiedo) así, Portuguese assim, Galician así, Catalan així (< eccum sic), French ainsi (< in sic), Italian così (< eccu sic), Istriot cussèi (< eccu sic), Romanian așa (< ac sic)
This word and its cognates in other Iberian Romance languages hark to an old dialect continuum in the Iberian peninsula. Catalan aixi, Romanian așa, and French si and ainsi come from similar but different Latin constuctions.