When something is at its onset, it's at the beginning, just getting started, and it's often something that's not so pleasant. The onset of hurricane season is probably not the best time to visit the beach.

If you catch an infection right at the onset and treat it immediately, the infection may not last so long. You can also have an early onset of something, and that usually means something you'd rather not have at all, as with early-onset Alzheimer's, a disease that usually appears after age 65. If you begin showing signs of the disease at a younger age than usual, you're said to have early-onset Alzheimer's.

Primary Meanings of onset

the beginning or early stages
(military) an offensive against an enemy (using weapons)
Full Definitions of onset

n the beginning or early stages

“the onset of pneumonia”
Type of:
the beginning of anything

n (military) an offensive against an enemy (using weapons)

attack, onrush, onslaught
September 11
the day in 2001 when Arab suicide bombers hijacked United States airliners and used them as bombs
show 58 types...
hide 58 types...
ground attack
an attack by ground troops
an impetuous rush toward someone or something
banzai attack, banzai charge
a mass attack of troops without concern for casualties; originated by Japanese who accompanied it with yells of `banzai'
diversion, diversionary attack
an attack calculated to draw enemy defense away from the point of the principal attack
incursion, penetration
an attack that penetrates into enemy territory
blitz, blitzkrieg
a swift and violent military offensive with intensive aerial bombardment
an attack that is intended to seize or inflict damage on or destroy an objective
counterattack, countermove
an attack by a defending force against an attacking enemy force in order to regain lost ground or cut off enemy advance units etc.
bombardment, bombing
an attack by dropping bombs
fire, firing
the act of firing weapons or artillery at an enemy
an attack of machine-gun fire or cannon fire from a low flying airplane
coup de main, surprise attack
an attack without warning
diversionary landing
an amphibious diversionary attack
a retaliatory charge
the action of penetrating between or among
a penetration of a barrier such as an enemy's defense
the act of invading; the act of an army that invades for conquest or plunder
a process in which individuals (or small groups) penetrate an area (especially the military penetration of enemy positions without detection)
foray, maraud, raid
a sudden short attack
first strike
the initial use of nuclear weapons to attack a country that also has nuclear weapons; considered feasible only when the attacker can destroy the other country's ability to retaliate
surgical strike
an attack (usually without prior warning) intended to deal only with a specific target
preventive attack, preventive strike
a strike that is carried out in order to deter expected aggression by hostile forces
bombing run
that part of the flight that begins with the approach to the target; includes target acquisition and ends with the release of the bombs
area bombing, carpet bombing, saturation bombing
an extensive and systematic bombing intended to devastate a large target
antiaircraft fire
firing at enemy aircraft
barrage, barrage fire, battery, bombardment, shelling
the heavy fire of artillery to saturate an area rather than hit a specific target
the simultaneous firing of all the armament on one side of a warship
burst, fusillade, salvo, volley
rapid simultaneous discharge of firearms
call fire
fire delivered on a specific target in response to a request from the supported unit
cover, covering fire
fire that makes it difficult for the enemy to fire on your own individuals or formations
concentrated fire, massed fire
fire from two or more weapons directed at a single target or area (as fire by batteries of two or more warships)
fire intended to neutralize or destroy enemy weapons
counterpreparation fire
intensive prearranged fire delivered when the immanence of enemy attack is discovered
fire from two or more points so that the lines of fire cross
destruction fire
fire delivered for the sole purpose of destroying material objects
direct fire
fire delivered on a target that is visible to the person aiming it
distributed fire
fire dispersed so as to engage effectively an area target
fratricide, friendly fire
fire that injures or kills an ally
hostile fire
fire that injures or kills an enemy
grazing fire
fire approximately parallel to the ground; the center of the cone of fire does rise above 1 meter from the ground
harassing fire
fire designed to disturb the rest of enemy troops and to curtail movement and to lower enemy morale
indirect fire
fire delivered on a target that is not itself used as the point of aim for the weapons
interdiction fire
fire directed to an area to prevent the enemy from using that area
neutralization fire
fire that is delivered in order to render the target ineffective or unusable
observed fire
fire for which the point of impact (the burst) can be seen by an observer; fire can be adjusted on the basis of the observations
preparation fire
fire delivered on a target in preparation for an assault
radar fire
gunfire aimed a target that is being tracked by radar
registration fire
fire delivered to obtain accurate data for subsequent effective engagement of targets
scheduled fire
prearranged fire delivered at a predetermined time
searching fire
fire distributed in depth by successive changes in the elevation of the gun
supporting fire
fire delivered by supporting units to protect or assist a unit in combat
suppressive fire
fire on or about a weapon system to degrade its performance below what is needed to fulfill its mission objectives
unobserved fire
fire for which the point of impact (the bursts) cannot be observed
artillery fire, cannon fire
fire delivered by artillery
(fencing) a counterattack made immediately after successfully parrying the opponents lunge
terrorist attack
a surprise attack involving the deliberate use of violence against civilians in the hope of attaining political or religious aims
ambuscade, ambush, lying in wait, trap
the act of concealing yourself and lying in wait to attack by surprise
pre-emptive strike
a surprise attack that is launched in order to prevent the enemy from doing it to you
Type of:
military operation, operation
activity by a military or naval force (as a maneuver or campaign)

Sign up, it's free!

Whether you're a student, an educator, or a lifelong learner, Vocabulary.com can put you on the path to systematic vocabulary improvement.