extemporal
The weavers design the patterns extemporally, based on traditional motifs that are passed down.
She extemporally began to sing a sad song.
He sang extemporally about the birth of the new princess.
He extemporally replied to her impolite question.
We should not preach extemporally, but think carefully before speaking.

SMART Vocabulary: related words and phrases

Not expected or planned
abrupt end
abrupt halt
abruptly
abruptness
ad hoc
inadvertency
inadvertent
inadvertently
inconceivable
inconceivably
sine die
spirit
spontaneity
spontaneous
spontaneously
unsuspected
untimely
untoward
unwilled
unwitting