Risible

risible [ˈri-zə-bəl]
adj. 1. capable of laughing; disposed to laugh; 2. arousing or provoking laughter; laughable; 3. associated with, relating to, or used in laughter

[Late Latin risibilis, from Latin risus, past participle of ridēre to laugh: 1557]

Risible is an excellent word that is not in common usage. I don't know why. Most people are risible. That is, they love to laugh. The only other English word I know directly related to risible is its noun form, risibility ("the ability or disposition to laugh; humorous awareness of the ridiculous and absurd").

Risible is not related to rise ("to get up from a lying, sitting, or kneeling posture"). When someone gets a rise out of you, he's not making you laugh. Rather, he's provoking anger or irritation.

I once had a roommate who was inordinately risible. He laughed all the time. He wasn't crazy. He was joyous ("experiencing, causing, or showing joy"). It was fun to watch a sitcom with him, because he laughed out loud at every opportunity. His laughter was infectious. I was happier around him. Sophisticates ("people who have a refined knowledge of the ways of the world cultivated especially through wide experience") scoff at television shows that employ a laugh track or a live audience that laughs at every joke, funny or not. I don't share that prejudice. All else held equal, a TV comedy is better to watch when you have others laughing along with you. Of course, if the show is not funny, canned laughter won't change that. But a laugh track will make watching a funny show more pleasurable.

Before the last of laugh -- its etymology is traced back to an onomatopoeic origin in Sanskrit, kakhati, but made it to English, 1557, by way of Anglian hlæhhan, earlier hlihhan, from Germanic klakhjanan -- there a number of good synonyms or near-synonyms to list: cacchination ("rauccous laughter"); cackle ("a loud laugh suggestive of a hen's cackle"); chortle ("a snorting, joyful laugh or chuckle"); chuckle ("to laugh quietly or to oneself"); gale ("a state of excitement, passion, or hilarity brought on by laughter); giggle ("to laugh with repeated short, spasmodic sounds"); guffaw ("a coarse laughter"); howl ("a loud, scornful laugh or yell"); roar ("to laugh loudly or boisterously"); snicker ("to laugh in a half-suppressed, indecorous or disrespectful manner."); snigger ("a disrespectful laugh"); tee-hee ("a sound made in imitation of a giggle or titter"); and titter ("to laugh in a restrained, self-conscious, or affected way, as from nervousness or in ill-suppressed amusement").