BEWARE
beware, mind
(verb) be on one’s guard; be cautious or wary about; be alert to; “Beware of telephone salesmen”
Source: WordNet® 3.1
Etymology
Verb
beware
(defective, ambitransitive) To use caution, pay attention to (used both with and without of).
Usage notes
The verb was traditionally used without of (e.g. "beware the ides of March", from Julius Caesar Act 1, scene 2, 15–19, by Shakespeare), but it is often used with the preposition today.
The verb beware has become a defective verb and now lacks forms such as the third-person singular simple present bewares and the simple past bewared. It can only be used imperatively (Beware of the dog!), subjunctively (It's important that he beware of the dog), or as an infinitive (You must beware of the dog or They told me to beware of the dog).
The inflected forms bewares, bewared, and bewaring are called obsolete in Fowler's Dictionary of Modern English Usage, along with the simple indicative "I beware". The forms bewares and bewared are very rarely found in modern texts, though bewaring is slightly less rare. These inflections are more likely to be found in very old texts.
The meanings of the obsolete inflected forms can be easily understood by replacing "beware" with the more modern equivalent consisting of a conjugated form of "be" and the word "wary". For example "bewares" means the same as "is wary", "bewared" the same as "was wary", etc.
Source: Wiktionary
Be*ware", v. i. Etym: [Be, imperative of verb to be + ware. See Ware,
Wary.]
1. To be on one's guard; to be cautious; to take care; -- commonly
followed by of or lest before the thing that is to be avoided.
Beware of all, but most beware of man ! Pope.
Beware the awful avalanche. Longfellow.
2. To have a special regard; to heed. [Obs.]
Behold, I send an Angel before thee. . . . Beware of him, and obey
his voice. Ex. xxiii. 20, 21.
Note: This word is a compound from be and the Old English ware, now
wary, which is an adjective. "Be ye war of false prophetis." Wyclif,
Matt. vii. 15. It is used commonly in the imperative and infinitive
modes, and with such auxiliaries (shall, should, must, etc.) as go
with the infinitive.
Be*ware", v. t.
Definition: To avoid; to take care of; to have a care for. [Obs.] "Priest,
beware your beard." Shak.
To wish them beware the son. Milton.
Source: Webster’s Unabridged Dictionary 1913 Edition