a. Colus (F.), distaff; domus (F.), house (see § 93), and many names of plants in -us, vary between the Second and Fourth Declensions.
b. Some nouns vary between the Second and Third: as, iúgerum, -í, -ó, ablative -ó or -e, plural -a, -um, -ibus; Mulciber, genitive -berí and -beris; sequester, genitive -trí and -tris; vás, vásis, and (old) vásum, -í (§ 79. e).
c. Some vary between the Second, Third, and Fourth: as, penus, penum, genitive pení and penoris, ablative penú.
d. Many nouns vary between the First and Fifth (see § 98. c).
e. Some vary between the Third and Fifth. Thus, - requiés has genitive -étis, dative wanting, accusative -étem or -em, ablative -é (once -éte); famés, regularly of the third declension, has ablative famé (§ 76. N. 1), and púbés (M.) has once dative púbé (in Plautus).
f. Pecus varies between the Third and Fourth, having pecoris, etc., but also nominative pecú, ablative pecú; plural pecua, genitive pecuum.
g. Many vary between different stems of the same declension: as, femur (N.), genitive -oris, also -inis (as from femen); iecur (N.), genitive iecinoris, iocinoris, iecoris; múnus (N.), plural múnera and múnia.