[2] In German, the interfix -s- has to be used between certain nouns in compound words, but not all, such as Arbeitszimmer ("workroom") as opposed to Schlafzimmer ("bedroom").
This originates from the masculine and neuter genitive singular suffix -s. German has many other interfixes, for example -es, -(e)n-, -er- and -e-.
In other compounds the -e- stems from a case suffix: petekind ("godchild") from peet ("godfather") and kind ("child").
For example, brod + gradilište = brodogradilište ("shipyard"), but kuća + pazitelj = kućepazitelj ("concierge").
Unless an interfix is added, the new-formed word is considered to be a word-joining, such as zimzelen (zima + zelen, "evergreen").