-eren
There are a few nouns to which we have to add -eren instead of -en:
het kind | de kind eren | the child(ren)
het kalf | de kalv eren | the calves
het ei | de ei eren | the eggs
het gemoed | de gemoed eren | the moods
het goed | de goed eren | the goods
het lam | de lamm eren | the lambs
het lied | de lied eren | the songs
het rund | de rund eren | the oxen
het volk | de volk eren | the peoples
Note the doubled 'm' in lammeren (see [keeping vowels short](#/lesson/SpellingAndPronunciation.21)) and the _f_ that turned into _v_ in kalveren (see [hard and soft consonants](#/lesson/SpellingAndPronunciation.23)).
The noun 'het been' gets an extra _d_:
het been | de beend eren | the bones
'Been' has two different meanings: 1. bone and 2. leg. If it refers to a leg, the noun has a regular plural:
_het been_ | _de benen_ | _the legs_
'Het blad' is irregular because we let the short vowel in the singular turn into a long one in the plural. The plural's syllables are separated by dashes so that you can see that the letter a is now a single open vowel. The regular spelling rules dictate that the _d_ be doubled to keep the vowel short.
het blad | de bla-d e-ren | the leaves
het blad | de bla-den | the sheets (of paper)
Both plurals are irregular. The regular plural form would have been bla dd en.
-a
Latin nouns that end in -um get - _s_ in the plural. Some nouns can also take -a instead of s. The -a ending comes in the place of -um.
het museum | de muse ums / muse a | the museums
het stadium | de stadi ums / stadi a | the phases
het podium | de podi ums / podi a | the (theater) stages
het aquarium | de aquari ums / aquari a | the aquariums
The same can happen to words that end in -on, a less common ending in Dutch.
het stadion | de stadi ons / stadi a | the stadions