geest en gemoed

de geest – mind, consciousness; spirit; character
het gemoed – mind, heart


-icus/-ici plural form

I’ve noticed that some words, which seem to have Latin origin, form their plurals in an unusual way:

Singular: technicus
Plural: technici

Singular: historicus
Plural: historici

Singular: mathematicus
Plural: mathematici

Singular: informaticus
Plural: informatici

Singular: academicus
Plural: academici

Singular: diabeticus
Plural: diabetici