(3) Mutation-plurals.

SINGULAR. PLURAL.
Nom. fōt (foot). Nom. fēt.
Dat. fēt. Dat. fōt-um.
Gen. fōt-es. Gen. fōt-a.

So also tōþ (tooth). Mann (man), męnn, mannes; męnn, mannum, manna.

(4) u-nouns.

SINGULAR. PLURAL.
Nom. sun-u (son). Nom. sun-a.
Dat. sun-a. Dat. sun-um.
Gen. sun-a. Gen. sun-a.

So also wudu (wood).

(5) r-nouns (including feminines).

SINGULAR. PLURAL.
Nom. mōdor (mother). Nom. mōdor.
Dat. mēder. Dat. mōdr-um.
Gen. mōdor. Gen. mōdr-a.

So also brōþor (brother); fæder (father), dohtor (daughter), have dat. sing. fæder, dehter.