Synonyms of the word 
VIGILANT → ALERT - ARGUS-EYED - OPEN-EYED - WAKEFUL - WATCHFUL
vigilant
- adj. Watchful, especially for danger or disorder; alert; wary.
alert
- adj. Attentive; awake; on guard.
- adj. (obsolete) Brisk; nimble; moving with celerity.
- n. An alarm.
- n. A notification of higher importance than an advisory.
- v. To give warning to.
argus-eyed
- adj. ever vigilant.
open-eyed
- adj. alert and vigilant.
wakeful
- adj. Awake; not sleeping.
- adj. Sleepless.
- adj. Vigilant and alert; watchful.
watchful
- adj. observant, vigilant and aware.
If you are interested in words, visit the following sites :
- wiktionary.org/vigilant For complete definition of a word
- 1word.ws/vigilant to play with words, suffixs, prefixs, etc.