Definition from Wiktionary, the free dictionary
jugular (not comparable)
- Relating to, or located near, the neck or throat.
- (zoology, of fish) Having ventral fins attached under the throat.
- (humorous) Relating to juggling.
relating to the neck or throat
jugular (plural jugulars)
- Vein through the neck (or thorax) that returns blood from the head back towards the heart. Properly this is called the jugular vein.
- By extension, any critical vulnerability.
- It was vicious; he went for the jugular.
Usage notes 
The plural form jugulars is almost never used.
- One of Lionel's old Salthill friends with whom he exchanged perhaps a dozen words a year, and with whom he sometimes played squash, and tennis, both men killers on the court, seeking the jugular [...]. - "Middle Age : A Romance" (2001) by Joyce Carol Oates (Fourth Estate, paperback edition, 83)
Derived terms 
vein through the neck — see jugular vein