The word Χριστούγεννα is a composite one from the genitive case of the name Χριστός (του Χριστού= Christ’s) and the noun η γέννα (=the birth). It is the birth of Christ, therefore Χριστούγεννα means the day when Christ was born. Did you know that the prefix gen- and the suffix -gen come from the Greek root γεν-, which means becoming, give birth to?

THE GREEK -GEN- IN ENGLISH
English word Greek word Pronunciation
gene το γονίδιο to yoNEEdio
gender το γένος to YEnos
genealogical ο γενεαλογικός o yenealoyiKOS
genealogy η γενεαλογία ee yenealoYEEa
genesis η γένεσις ee YEnesis
genetic ο γενετικός o yenetiKOS
genetically γενετικά yenetiKA
genetics η Γενετική ee yenetiKEE
genotype ο γονότυπος o yoNOtipos
genotypic ο γονοτυπικός o yonotipiKOS
genius ο ιδιοφυής o idiofiEES
oxygen το οξυγόνο to oxiYOno
hydrogen το υδρογόνο to idroYOno
The suffix -gen indicates that which produces, or something produced. In Chemistry it is used to indicate certain elements: oxygen, hydrogen, nitrogen.

IS THE WORD GENIUS A GREEK ONE?
The English word genius also derives from the above Greek root. In the beginning it meant attendant spirit present from one’s birth, the innate ability or inclination. This meaning led to a sense of a person’s natural ability, and finally since the mid-17th century it means the exceptional natural ability. In Greek we use the word genius, transliterated into Greek «Είναι τζίνι» or we say «Είναι ιδιοφυής», which verbatim also means of exceptional natural ability.

Ο ΓΟΝΟΣ, gono-
The prefix gono- and the suffix -gony (heterogony) come from the Greek word ο γόνος (o YOnos), which means the offspring, the seed, the production of. For instance, gono-coccus is a bacterium which causes the disease gono-rrhea, and hetero-gony is the alternation of parthenogenetic and sexual generations in rotifers and similar animals.
In Greek we say «Είναι γόνος καλής οικογένειας.» = «He is an offspring of a good family.»
Note that English words ending in -gon, like the pentagon, the hexagon, derive from the Greek word gonia, γωνία = angle (yoNEEa) and not from γεννώ (= give birth to). Thereafter, the word pentagon indicates a shape with five angles and hexagon a shape with six angles.

Η ΓΕΝΝΗΣΗ ΚΑΙ Η ΓΕΝΕΣΙΣ
In ancient and modern Greek too, we have two different verbs which etymologically come from the root γεν-, which means coming to be. The verbs γίγνομαι and γεννάω. The first, γίγνομαι in ancient Greek and γίνομαι (YEEnome) in modern Greek, expresses the process of existence, a becoming. From this verb derives the word genesis, η γένεσις in ancient Greek, η γένεση (ee YEnesi) in modern Greek. The second verb γεννάω, (yeNAo) expresses the act of engendering, of giving birth to something, of bringing something into being. From the verb γεννάω derive the words η γέννα (ee YEna), η γέννηση (ee YEnisi). Philologists haven’t reached a conclusion why η γένεση is written with one ν and η γέννηση with two.

EXAMPLES
Η γέννηση του Χριστού. (EE YEnisi too hriSTOO). The birth of Christ.
Η γένεση του κόσμου. (EE YEnesi too KOsmoo). The genesis (creation) of the world.
Η μαμά μου γέννησε εμένα. (EE maMA moo YEnise eMEna). My mother gave birth to me.
Η μαμά μου γέννησε την αδελφή μου /τον αδελφό μου. (EE maMA moo YEnise teen adelFEE moo /ton adeLFO moo). My mother gave birth to my sister /to my brother.

PRONUNCIATION KEY
i (idiom), ee (needle), e (energy), o (organism), oo (boot), y (yes), h (helium), th (theory), d (the). The capitalized syllables are accented.