West European linguistic stuff that seems so obviously Basque that it hurts:
- bi-, "Latin" preffix meaning "two" or "twice", very much extended to other European languages. < Basque bi (two), maybe via Ligurian or some other pre-IE Italian language.
- sardine and related Sardinia. < sardin(-a/-e) (sardine) < sarda (fish school) + -in ('doer', 'maker', probably from verb egin: to do, to make)
General West IE:
- -er/-ero, suffix indicating profession (i.e. carpenter) < proto-Germanic *-arjoz OR Latin -arium < Basque -ari (professional suffix) < ari (auxiliar verb of action) <> arin (quick, fast) <> aritu (to hurry)
- ill and kill - oddly similar to Basque hil (pronounced like ill, to die or to kill) < proto-Vasco-Aquitanian *kil (h, silent in the South but aspired in the North, seems to derivate from lost k - or g). Mediated by old Norse illr apparently in the case of ill (but not kill, whose etymology is uncertain).
- to as particle for infinitive verbs (i.e. to do). While it might have a precedent in old Anglosaxon, it does not seem to have any other Indoeuropean cognate with this meaning of verbal particle. But in Basque it is one (and the most common) of three infinitive suffixes: -tu (pronounced exactly like to), -i and -n.
I also considered ash (Basque auts) but this one seems to have legitimate Indoeuropean origins (Sanskrit asa and others) and could be a borrowing by Basque or whatever else (I'm not discarding remote shared origin of Basque and Indoeuropean, which would be less surprising than the unlikely Dene-Caucasian hypothesis, honestly).
Another word I have wondered about in English is black, which looks similar to Basque beltz, same meaning (compound variant bel-/-bel as in beldur (fear) or urbel (blackwater, a river near Burgos), vide also bele: raven), which could be from a conjectural Vascoid root *belaK. However there's an alternative etymology related to blank and, via that word, to Romance blanc, blanco (white), via highly conjectural proto-Germanic *blakaz < PIE *blegh (no other known derivatives, it seems). So uncertain.
- Castilian izquierda, Catalan esquerra, Galician/Portuguese esquerda < Basque ezker (left) or Iberian iskeŕ (argued to mean left or hand), and maybe related to Basque esker(-tu), meaning to thank (also eskerrak, eskerrik mean thanks as noun, pl. - never found in singular form, same in this aspect to what happens in other languages of West Europe: gracias, thanks...). Oddly enough some linguists reject this etymology biased by the negative perception of the left hand in Indoeuropean and particularly Latin (sinestra), which does not seem to exist in Basque (see the discussion at Vasco-Caucasian blog by promising Catalan linguist Octavià Alexandre)