I go to the gym twice a week.

Involving two occurrences or instances.
She called me twice yesterday.
He read the book twice.
They visited the museum twice.
twice a day
twice as much
twice a week
double
dually
twofold
She called me twice yesterday.

On two occasions or times.
He visited the museum twice last month.
I have read that book twice.
They met twice a week for practice.
twice a day
twice as much
twice the size
two times
double
dually
I have seen that movie twice.

Two times; on two occasions.
I called her twice yesterday.
He visited the museum twice last month.
They practiced the song twice before the performance.
twice a week
twice as much
twice the size
two times
double
dually