This is the 4514th most frequent Russian word.
вызова
"Вызова" means "challenge" or "summons" in English, depending on context.
The word 'вызова' here is used as a genitive singular form of 'вызов', meaning 'challenge'.
Принятие этого вызова стало началом великих перемен.
Accepting this challenge marked the start of great changes.
Here, 'вызова' is part of the phrase 'вызова врача', indicating 'calling (of) the doctor'.
После вызова врача больной почувствовал себя лучше.
After calling the doctor, the patient felt better.
The word 'вызова' again appears in its genitive form, used here to connect with the word 'угрозы' to mean 'challenges' in the context of handling difficulties.