The word Ȝecyndbēc is defined by the Dictionary of Old English (under the spelling gecyndboc) as:
Genesis, literally understood as the book of creation or begetting
It is made of two words: bec/boc (book) and Ȝecynd/gecynd, the latter of which has no modern equivalent but is a combination itself of the prefix ge-/ȝe- (also has no modern English equivalent) and kind. In Old English the word gecynd had several different related meanings (according to the OED) including family, gender/sex, genitals, and progeny.
Actually “Genesis” was also used in Old English. Ælfric writes:
seo boc ys gehaten Genesis, þæt ys gecyndboc, for þam þe heo ys firmest boca & spricþ be ælcum gecinde.
“The book is named Genesis, that is gecyndboc...”