This is the 502nd most frequent Czech word.
nová
"Nová" means "new" (feminine form) in English.
'Nová' in this context is an adjective describing the feminine noun 'kniha', matching its grammatical gender, case, and number.
Tato nová kniha je velmi zajímavá.
This new book is very interesting.
'Nová' in this sentence is an adjective modifying the neutral plural noun 'auta', indicating its agreement in gender, case, and number.
Koupil jsem nová auta pro firmu.
I bought new cars for the company.
'Nová' functions as an adjective describing the plural nominal 'pravidla', agreeing in gender, case, and number.