Learner's definition of HASTEN
to cause (something) to happen more quickly
A factory was built, hastening [=accelerating] the town's growth.
His death was hastened by alcohol abuse.
to move or act quickly
hasten to add/say/explain (etc.)
to immediately say something in order to prevent confusion or misunderstanding
The company announced that the initial tests look promising, but they hastened to add that there is still much more testing to be done.
Let me hasten to point out that these changes will not affect our existing clients.