This is the 13592nd most frequent Russian word.
невозможным
"Impossible."
Here, 'невозможным' functions as a predicate in a sentence constructed with 'оказывается' to describe an outcome.
Это оказалось невозможным из-за погодных условий.
It turned out to be impossible due to weather conditions.
'Невозможным' acts as an object predicate describing what is being considered.
Считать это невозможным — значит лишать себя надежды.
To consider this impossible is to deprive oneself of hope.
The word 'невозможным' serves as a descriptive adjective in a predicate construction following 'казалось'.