The last line of the quatrain of the famous German nursery rhyme “Müde bin ich” is “Über meinem Bette sein.” Why is the plural being used there? Or is it a different form of “das Bett”?
The final "e" in "Bette" indicates the dative case and is not a plural form. It normally isn't used in contemporary German anymore, however there are some fixed expressions like "zu Hause" where it is still encountered nowadays.
Über meinem Bette.
is singular and equivalent to
Über meinem Bett.
and the plural is
Über meinen Betten.
über meinem Bette sein
Bette is not plural. It's an antiquated dative singular often found in poetry.
(from the wikipedia article about Dative case, emphasis mine)
In general, the dative (German: Dativ) is used to mark the indirect object of a German sentence. For example:
- Ich schickte dem Mann(e) das Buch. (literally: I sent "to the man" the book.) – Masculine
- Ich gab der Frau den Stift zurück. (literally: I gave "to the woman" the pencil back.) – Feminine
- Ich überreiche dem Kind(e) ein Geschenk. (literally: I hand "to the child" a present.) – Neuter
In English, the first sentence can be rendered as "I sent the book to the man" and as "I sent the man the book", where the indirect object is identified in English by standing in front of the direct object. The normal word order in German is to put the dative in front of the accusative (as in the example above). However, since the German dative is marked in form, it can also be put after the accusative: Ich schickte das Buch dem Mann(e). The (e) after Mann and Kind signifies a now largely archaic -e ending for certain nouns in the dative. It survives today almost exclusively in set phrases such as zu Hause (to the house, lit. going home), im Zuge (in the course of), and am Tage (in the afternoon), as well as in occasional usage in formal prose, poetry, and song lyrics.
Note: am Tage doesn't mean in the afternoon, but on the day (am Tage des Jüngsten Gerichts = on the Day of Judgement) or during daytime. The translation of zu Hause is also questionable.