From Proto-Finnic *-lek or *-llek, probably a variant of *-len or *-llen (whence dialectal -len, -llen), which is related to *-sen (illative case suffix) and probably -l- (external locative suffix) + -en of unknown origin and meaning, possibly from Proto-Uralic *-n (dative suffix) or *-ŋ (lative suffix).
It is not known whether the short *-l- or long *-ll- is original. If short, the long -l- may be due to analogy with -lla, -lta. The answer likely depends on the origin of the -l- itself. The traditional theory posits that it comes from the toponymic suffix *-la, but more recently it has been proposed that it is in fact a reduction of *ülä (“upper, above”); thus *...n *ül(ä)-nä > *...n-l-nä > *...lnä > *...llä. The initial genitive ending is lost by reduction of a phonotactically impossible sequence, but not in *...n-l-en > *...ll-en, hence *-llen.
- forms the allative case of a noun, adjective, numeral or pronoun