Sometimes, we use the connector -er for words that get -eren the plural for (see plural nouns).
| het kind + de wagen
| de kinderwagen
| the buggy
|
| het ei + de dooier
| de eierdooier
| the egg-yolk
|
| het kalf + de liefde
| de kalverliefde
| the ('calf') love between teenagers
|
| het rund + het gehakt
| het rundergehakt
| the minced beef
|
The connector -er is very uncommon. Even words that take -eren as a plural ending, usually get -e, -en, -s.
Next to kalverliefde, we also have kalfskarbonade (veal-cutlet), next eierdooier also eiwit (protein) and eicel (egg-cell), and next to rundergehakt also rundvlees (beef).
Questions? 
