Couldn't find its etymology... anyone knows?
What does its meaning break down to?
Also, when should it be used best?
Thanks.
In modern usage, to have at is to attempt, to go ahead, or to attack physically. I suspect it comes from a shortening of the phrase have a go (at), which is used in the very same situations. Have at it means try (to do) it, have at thee! announces an attack in Shakespearian English, and he had at her with a knife means he attacked her with it.
Straitdope's forum suggests
The phrase "have at avail" means to have at an advantage and the earliest citation is to Malory (Le Morte D'Arthur) in the phrase* "Him thought no worship to have a knight at such avail, . . ."
Apparently "have at you" (or similar) appears in several Shakespeare plays in the sense of: let battle commence.
The OED dates "have at" to the 14th century:
V 27 b. intransitive. With at. To go at, esp. aggressively or forcefully; to tackle or attack; (also) to make an attempt at, ‘have a go at’. In early use chiefly in imperative, frequently with first-person meaning: ‘let me at (you, it, etc.)’, ‘here goes’ (now archaic). Formerly also with other prepositions (and adverbs), as †after, †among.
c1400 (▸?c1390) Sir Gawain & Green Knight (1940) l. 2288 ‘Haf at þe þenne,’ quoþ þat oþer. [trans "Have at thee then," said the other one.]
1639 T. Fuller Hist. Holy Warre iii. xi. 128 He wintered in Askelon, intending next spring to have at Jerusalem.
1916 J. Galsworthy Sheaf 298 One would not admit a physical defeat, but clench the teeth and have at it again.
2009 New Yorker 2 Feb. 50/3 After the tabloids and the upstate papers had at her, she attended another friend's birthday party.
What does its meaning break down to?
The "at" was probably
OED
- At a person (Latin apud):
†a. In personal contact with; in the immediate presence or company of. Obsolete (repl. by with, by, beside, in presence of, before).
c1275 (▸?a1200) Laȝamon Brut (Calig.) (1978) l. 12621 We woren..at [c1300 Otho mid] Arðure þan kinge. [We were with Arthur the king.]
The idea could be that the threated blow, etc., would be in contact with the person threatened.
Also, when should it be used best?
Some time prior to 1900. It is now archaic.
NB, have at is not a shortening of "have a go at", which is a much later (late 18th c.) construction.
P1. Chiefly colloquial. to have a go.
a.(a) Chiefly with at. To aim a blow or shot at someone or something; to make an attack or onslaught upon someone or something.
1792 Lady's Mag. May 244/1 I felt such a flow of spirits and courage, that I hid myself behind a tree, determined to have a go at him—the moment he passed me, I fired my pistol.