hilar-

(Greek > Latin: cheerful, gay, joyful, good spirits)

accelerate, exhilarate
accelerate, verb (AK SEL uh rayt") (verb)
1. To cause anything in motion or process to go or move faster; to speed up: To avoid being hit by the truck, Harvey had to accelerate his car.
2. To cause to happen sooner; to hasten: Resting will often accelerate a person’s recovery from an illness.
exhilarate, verb (ig ZIL uh rayt") (verb)
To cause someone to feel very happy and excited: Knowing that their daughter, Bernice, has passed her exam will certainly exhilarate the parents.

When Darren will accelerate his car on the highway, the rush of air through the window will serve to exhilarate him; however, he needs to remember that excessive speed can also accelerate the process of getting a speeding ticket.

accelerator, exhilarator
accelerator (ak SEL ur ay" tur) (noun)
A pedal or other device to make something go faster, to speed up, quicken the pace: Claude suddenly stepped too hard on the accelerator of his car and ran it into a tree.
exhilarator (eg ZIL uh ray" tur) (noun)
That which cheers up, enlivens, stimulates, and delights: The manager of the hotel told Jim and Jane that it would be a real exhilarator if they were to go for a walk in the beautiful woods nearby and get some fresh air.

Stepping on the accelerator and moving at great speed is often an exhilarator to people; that is, until they get caught in a speed trap.

exhilarant
exhilarate (eg ZIL uh rayt")
Make merry or lively; put into high spirits; cheer: "Seeing friends and exchanging gifts during the holiday season exhilarates us all."
exhilaratingly
exhilaration
exhilarative
exhilarator (eg ZIL uh ray" tur)
That which cheers up, enlivens, stimulates, invigorate, delights: "We were told that it would be a real exhilarator if we were to go for a walk in the beautiful woods and fresh air."

Exhilarate comes from the Greek element hilaros, "cheerful", which also gives us hilarious, "causing so much cheerfulness that people break out laughing.

hilarious
hilariously
hilariousness
hilarity