köken: The first part is from vic-, vicis (“alternation, turn”) and the final part is from the adverb-forming suffix -tim (etymologically the adverbial accusative of the i-stem abstract noun suffix *-tis), but the details of its formation are unclear. The -ss- would be expected to go back to original *-t-t- or *-d-t-, hence pre-forms such as *vici-dtim (a compound with the root of dō, dare, dedī, datum)…