Johan Schalin’s site has a discussion of early IE loanwords in Finnish.
(After reading that, use the tabs “On substitutions”, “Abbreviations” and “To the Lexicon").
Finnish has sometimes been compared to a “freezer” because once a word was borrowed it has often changed much less than its original.
For example the word kuningas ‘king’ gives us independent information about Proto-Germanic, validating the data produced by theoretical reconstruction methods. In much the same way the Finnish word kulke- ‘to go, wander, move’ gives us valuable independent information about Proto-Indo-European (PIE) , for which a verb root *kw(e)lH-e- (*kw(e)lH-o-) ‘go, wander, move’ has been reconstructed.
I’ve never previously thought about early PIE loanwords in non-PIE languages being used in reconstructive efforts. I found it an interesting read.