Frequency: The word is one of the 1500 most common words in English.
1.
A ~ change is one that happens very quickly.
...the country’s ~ economic growth in the 1980’s...
...the ~ decline in the birth rate in Western Europe.
ADJ: usu ADJ n
~ly
...countries with ~ly growing populations...
= fast
ADV: usu ADV with v, also ADV adj
~ity
...the ~ity with which the weather can change.
= speed
N-UNCOUNT
2.
A ~ movement is one that is very fast.
He walked at a ~ pace along Charles Street.
...whether the Tunnel will provide more ~ car transport than ferries...
ADJ: usu ADJ n
~ly
He was moving ~ly around the room...
= quickly
ADV: ADV with v
~ity
The water rushed through the holes with great ~ity.
= speed
N-UNCOUNT