Sigh, sorry I'm failing in my duty as Stormborn's research monkey. Maybe this will make up for it.
From the OED, 2d edition:
"[ME. gunne, gonne (riming with sonne = sun); hence already in 14-15th c. the word was adopted as Welsh gwn, Irish (also Sc. Gaelic) gunna, Anglo-L. gonna, gunna.
With regard to the ultimate etymology, a suggestion has been made by Prof. Skeat that ME. gunne may represent a hypocoristic form of a Scandinavian female name compounded with Gunn-. This conjecture receives a strong confirmation from the fact (communicated to us by Mr. W. H. Stevenson) that an account of munitions at Windsor Castle in 1330-1 (Exchequer Accts. Q.R. Bundle 18, no. 34, Pub. Rec. Office) mentions ‘una magna balista de cornu quæ vocatur Domina Gunilda’. There are other instances of the practice of bestowing female personal names on engines of war; but there was no distinguished lady named Gunilda (= ON. Gunnhild-r; spelt Gunnild in Havelok) in the 14th c., and it seems highly probable that this use of the name may have come down from Scandinavian times, when its exceedingly appropriate etymology would be understood (both gunn-r and hild-r mean ‘war’). If Gunnhildr, as is likely, was a name frequently given to ballistæ and the like, it would naturally, on the introduction of gunpowder, be given also to cannon. Indeed, there is some appearance of evidence that an explosive engine was actually called by this name many years before the earliest recorded instance of the use of gunpowder in warfare. The ‘song against the retinues of the great people’ in Pol. Songs (Camden) 237, which must have been written in the reign of Edw. II, contains the following passage:‘The gedelynges were gedered Of gonnylde gnoste; Palefreiours ant pages, Ant boyes with boste, Alle weren y-haht Of an horse oste’. The correct translation of this passage, which has hitherto been unexplained, seems to be as follows:‘The lackeys were gathered out of Gunnild's spark [OE. gnást: see GNAST n.]; the grooms and pages, the varlets with their boasting, all were hatched of a horse's dung’. According to analogy, the regular ‘pet-name’ in ON. for Gunnhild-r would be *Gunna, which would give Gunne in ME.; Rietz Sv. dial.-lex., mentions Gunne as a female Christian name still surviving in Swedish country districts. (In Iceland Gunna is now common, but it is taken to stand for Gurún.)
The other suggestions that have been made as to the origin of the word are obviously unsatisfactory. The assumed OF. *mangonne, of which gonne has been supposed to be a shortening, is wrongly inferred from mangonneau MANGONEL, and is not philologically possible, unless as a back-formation. The F. gonne, large cask, does not occur before the 16th c., and is regarded by Littré as adopted from the Eng. gun. The conjecture that ME. gunne is of echoic origin perh. involves no impossibility, but it has no positive support, and little intrinsic probability.] "
Here are the definitions and the first instance of each:
"I. The weapon.
1. a. A weapon consisting essentially of a metal tube (massive enough to require to be mounted on a carriage or a fixed substructure) from which heavy missiles are thrown by the force of gunpowder, or (in later use) by explosive force of any kind; a piece of ordnance, cannon, ‘great gun’.
1339 in Riley Lond. Mem. (1868) 205 Item, in Camera Gildaulæ sunt sex Instrumenta de latone, vocitata Gonnes, et quinque roleres ad eadem. Item, peletæ de plumbo pro eisdem Instrumentis, quæ ponderant iiiic libræ et dimidium. Item, xxxii libræ de pulvere pro dictis Instrumentis.
[other examples omitted]
b. Guns are fired in honour of persons and events, at festivities, and as signals; in the navy, morning and evening gun, ‘warning-pieces’ fired at morning and evening respectively; hence taken to indicate the times at which these guns are fired.
1556 Chron. Gr. Friars (Camden) 51 The xxti day of the same monyth after came in the lorde amrelle of France un to Grenwych with xiiij. goodly gallys, and many other sheppes, and there was shotte many gonnys. Ibid. 62 On Bartylmew evyne was shott dyvers goonnes at the gattes in London.
[other examples omitted]
c. fig.
1535 LATIMER Serm. (1584) 2 What great peeces [sc. of ordnance] hath he [the devil] had of Bishoppes of Rome, which haue destroyed whole Citties and countries, and haue slayne and brent many! what great Guns were those!
[other examples omitted]
2. In the 15th c. used somewhat vaguely for a large engine of war, often translating words meaning ‘mangonel, ballista, battering-ram’. Obs.
The commonly cited example in K. Alis. 3268 is due to the scribe of the 15th c. Lincoln's Inn MS., the reading in MS. Laud 622 being gynnes.
c1400 Rom. Rose 4176 They ne dredde noon assaut Of ginne, gunne, nor skaffaut.
[other examples omitted]
3. a. (Originally HAND-GUN.) Any portable fire-arm, except the pistol; a musket, fowling-piece, rifle, etc. (Quot. 1495 may belong to sense 1.)
1409 Excheq. Accts. Q.R. Bundle 44 No. 17 (P.R.O.), iij. canons de ferro ove v. chambres, un handgone.
[other examples omitted]
b. A pistol or revolver. orig. U.S.
1744 A. HAMILTON Itin. (1907) 150 ‘Then surely you had needs ride with guns’ (meaning my pistols).
[other examples omitted]
[some modern usages omitted]
4. A missile hurled from an engine of war. Obs.
c1385 CHAUCER L.G.W. 637 Cleopatra, With grysely soun out goth the grete gonne, And heterly they hurtelyn al atonys, ffrom the top doun comyth the grete stonys.
[many other colloquial and transferred meanings omitted]"
Gee, if anyone's still reading at this point (hey, wake up, Stormborn! This was for your benefit!), can you guess what I used to do for a living?
Signed,
Stormborn's Research Monkey