Template:is-decl-noun-kell

Declension of is-decl-noun-kell
kell	singular		plural
	indefinite	definite	indefinite	definite
nominative	{{{1}}}kell	{{{1}}}kellinn	{{{1}}}katlar	{{{1}}}katlarnir
accusative	{{{1}}}kel	{{{1}}}kelinn	{{{1}}}katla	{{{1}}}katlana
dative	{{{1}}}katli / {{{1}}}keli*	{{{1}}}katlinum	{{{1}}}kötlum	{{{1}}}kötlunum
genitive	{{{1}}}kels	{{{1}}}kelsins	{{{1}}}katla	{{{1}}}katlanna

The dative form with -katli is older and considered by many more correct. The latter form, with -keli, is a later development, under influence from the other cases.