An enemy from the popular Half-Life series of video games, the gonome can be found specifically in Half-Life: Opposing Force.
In order to best understand what a gonome is, you might also want to look up the headcrab and zombie.
A gonome is the next phase in headcrab-induced mutation after the zombie phase: When a headcrab latches onto the nervous system of an unlucky human, it will subsequently gain control of its limbs and begin to meld their physiologies. The ensnared individual quickly becomes a half-alien zombie, a hollow meat puppet for the parasite attached. After two days of feeding, these zombies will, in turn, mutate into a much faster, larger and more alien zombie, called a gonome.
The gonome looks very much like its zombie contemporaries, only with a far bulkier, greener torso and stronger leg and arm musculature. Also, the vertical 'mouth' in the centre of its chest has widened considerably, extending nearly three feet from top to bottom. This maw is also more articulate, able to open wide enough to easily bite onto a full-grown human. The jutting ribs of the host have also been sharpened at points, creating makeshift fangs. The headcrab has also merged considerably into the host's flesh. As such, the gonome is more of a unique entity than a parasitic relationship between two.
The gonome is not a similar-but-advanced zombie in looks only. Gonomes behave quite similar to zombies as well, only with some advanced aspects. Gonomes, unlike zombies, are fast. Having spotted prey, they will run at them with startling speed. They will use their chest-mouth to bite prey, something that zombies cannot do. They are also considerably more durable.
The gonome's largest difference comes from their ability to reach into their chest-mouth and remove highly acidic, golf ball-sized chunks of mucus and flesh. Gonomes can toss these chunks at distant prey with a surprising amount of accuracy, injuring them considerably.
Gonomes exist wherever zombies do, but are most often found in secluded areas with a large amount of prey. These conditions allow a zombie to complete the mutation into a gonome unhindered.
The ingredients to best stopping a gonome are distance, cover, and heavy weaponry. If none of these are avaliable, the best course of action is to never stand still.