Wary means keeping your guard up because something might go wrong. The way you watch a dog you do not know, the second read of a contract, a cat edging round a stranger's hand.
It nearly always takes OF: wary of strangers, wary of easy promises, wary of anything advertised as free. A wary person is not frightened — they are calm and watching, and that is the difference between wary and scared. Warily is the adverb and wariness the noun: he stepped warily onto the ice. You can be wary about doing something, but wary of is the pairing that never sounds wrong. The word is the old adjective ware with a -y added, and ware has all but disappeared on its own.
1adjectivewaryCareful and watchful because of possible danger, trouble or dishonesty.
“Buyers are wary of houses that have been on the market a year.”
synonyms: cautious, guarded, watchful
Also accepted in games: cautious
Wary is the old adjective ware with the ending -y stuck on it. Ware has faded out of ordinary English, so wary now carries the whole idea by itself. The family runs back to a Proto-Indo-European root, *wer-.
Proto-Indo-European
*wer-
Middle English
ware
English
ware
English, today
wary
From the adjective ware + y. ware comes from Middle English ware. From Middle English ware, from Old English waru, from Proto-West Germanic waru, from Proto-Germanic warō (“attention”) as in beware, in the sense of “an object of care, a valuable”, from Proto-Indo-European wer- (“to watch, keep guard”), whence also ward. Cognate with stq Were (“an item for exchange, barter, or sale; ware”), Dutch waar (“goods offered for sale or use; ware”), German Ware (“ware”), Danish -, Norwegian Bokmål -, Norwegian Nynorsk vare (“ware”), Faroese vøra (“ware”), Icelandic - and Swedish vara (“ware”).
Etymology from Wiktionary, CC BY-SA