Princeton's WordNet

1. on guard, on one's guard(p), upon one's guard(p), on your guard(adj)

   vigilant

   "on guard against con artists"; "must remain on your guard in such a situation"

Wiktionary

1. on guard(Adjective)

   The starting position of a fencing bout; en garde.

2. on guard(Adjective)

   vigilant, alert

• wag staan, op jou hoede weesAfrikaans
• في الحِراسَهArabic
• нащрекBulgarian
• precavidoPortuguese (BR)
• ve střehuCzech
• auf der HutGerman
• være på vagtDanish
• προετοιμασμένοςGreek
• en guardia, en alertaSpanish
• (kaitseks) ettevalmistatudEstonian
• مواظب بودنFarsi
• valppaanaFinnish
• sur ses gardesFrench
• לַעֲמוֹד עַל הַמִשמָרHebrew
• तैयारHindi
• spreman, pripravanCroatian
• résen vanHungarian
• siagaIndonesian
• viðbúinnIcelandic
• in guardiaItalian
• 用心してJapanese
• 당번으로Korean
• budrus, atsargusLithuanian
• būt modramLatvian
• bersediaMalay
• op zijn hoedeDutch
• på vakt, forberedt påNorwegian
• czujnyPolish
• مواظب بودنPersian
• مواظب اوسهPashto
• precavidoPortuguese
• pregătitRomanian
• насторожеRussian
• v strehuSlovak
• pripravljenSlovenian
• spremaSerbian
• på sin vaktSwedish
• เตรียมพร้อมต่อสู้Thai
• hazırlıklı, tedbirliTurkish
• 保持警戒Chinese (Trad.)
• (бути) насторожіUkrainian
• مستعد، چوکس ہوناUrdu
• đề phòngVietnamese
• 警惕Chinese (Simp.)