The Proto-Indo-European language had this adjectival formation with a *u-ending. Two main derivational processes can be identified:
- Type1 is reduplication, like in *bebhru- ‘beaver’, from *bhru- ‘brown’.
- Type2 is suffixation, mostly by *ka, as in whelk
from *welu-ka ‘spiral-shaped shell’.
Derivative with new meaning: Old Indian parkatī- ‘sacred Ficus’ with -ati suffix.
Another deadjectival suffix -ka is shown in Old High German fereheih, langobard fereha ‘horse chestnut’ from *per(i)kika, O.Ice. fjorr m. ‘tree, man’; o-grade in O.H.G. forha ‘pine tree’, Old English furh; Old Icelandic fura f. ‘pine’, fy:ri n. ‘pinetree forest’, O.H.G. *forh-is.
This suggests that the root *kwerk- was originally some kind of adjective.