*ghrei-

ghrēi-, Proto-Indo-European root meaning "to rub." 

It forms all or part of: chrism; Christ; christen; Christian; Christmas; cream; grime; grisly; Kriss Kringle.

It is the hypothetical source of/evidence for its existence is provided by: Greek khriein "to anoint, besmear;" Lithuanian griejù "to skim the cream off;" Old English grima "mask, helmet, ghost," Middle Low German greme "dirt."