qualtagh is a word from Manx English meaning "The first person to enter a house on New Year's Day". Another term for the same concept is "first-footer". It's from Manx quaaltagh, which according to the OED literally means "someone who meets or is met". The OED says it is from Manx quaail "meeting", which is cognate with Scots Gaelic còmhdhail and Irish Gaelic comhdháil, both from Old Irish comdál, all meaning "meeting". comdál is formed from the prefix com- plus dál "meeting, assembly, court". The etymology of dál is disputed, but it might be from Proto-Indo-European *dʰeh₁- "to set, put".
*dʰeh₁- in the prefixed and suffixed form *kom-dʰh₁-yo- became Latin condiō "to season, flavour" (as in condiment) which according to the AHD combined with Old French salemine "salted food" to form salmigondis and English salmagundi ("a salad of chopped meat, anchovies, eggs, and onions"). It's worth noting that the OED says "obscure origin" for salmagundi.
*dʰeh₁- has all sorts of other reflexes, like Greek τίθημι "to put" as in thesis, Sanskrit dadhāti "to place" as in sandhi, and Latin facio "to do, make" as in fact, affect and face. In English it became do, doom and deed.