Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
spec [spɛk] n (inf)
on spec(buy, go etc) науда́чу
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.
speck [spɛk]
n (of dirt) пя́тнышко; (of dust) кра́пинка# * is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.