precursor

esiaste

edelläkävijä That which precurse precurses, a forerunner, a predecessor, an indicator of approaching events.
{{quote-magazine|year=2013|month=September-October|author=http://www.americanscientist.org/authors/detail/katie-l-burke Katie L. Burke
puhekieltä One of the chemical compound|compounds that participates in the chemical reaction that produces another compound.
(l)
English precursor
(l); (l) (gloss)
(l) (gloss)
precursory, preceding