Called a preposition. This would seem to be bang (“precisely”) (just added) + on. Same problem as many multiword entries beginning with all and certain other adverbs. DCDuringTALK 11:48, 22 August 2011 (UTC)
Though it can be re-expressed many ways using 'on' as the last word, I'm not sure how we can cover this in a way that makes this sum of parts. Examples include dead on, and smack on. In other words, I remain unconvinced. Mglovesfun (talk) 12:13, 22 August 2011 (UTC)
Right is a fairly exact synonym for bang in this usage. MWOnline doesn't seem to have any trouble. They use a non-gloss definition as they do for most simple prepositions: used as a function word to indicate a time frame during which something takes place <a parade on Sunday> or an instant, action, or occurrence when something begins or is done <on cue> <on arriving home, I found your letter> <news on the hour> <cash on delivery>. DCDuringTALK 13:26, 22 August 2011 (UTC)
Furthermore, one of the usage examples uses on the dot which is itself an idiom even in the opinion of the editors of MWOnline (one of the least inclusive of MWEs). But perhaps someone can attest to the spelling bangon and invoke WT:COALMINE. DCDuringTALK 13:41, 22 August 2011 (UTC)
By fixing attention on the time aspect of the preposition on, we seem to be ignoring staple phrases such as Bang on the nose. and Bang on target. Not to forget the simple exclamation Bang on!!. -- ALGRIFtalk 14:49, 22 August 2011 (UTC)
bang on is not part of this. BTW, it is not really an expression of emotion and thus not really an interjection by my lights. It is a colloquial ellipsis of a sentence and should probably be under the L3 header "Phrase".
I simply assumed that MG's problem with the definition of on had to do with its temporal senses rather than its spatial senses. I usually find the physical sense of prepositions obvious, the spatial ones sometimes less so, and the more "grammatical" ones much, much less so. on the nose and on target are also themselves idioms. "Bang" seems to go well with other idiomatic (or nearly so) prepositional phrases like to rights, on the spot, on the mark, and in form (“of horses”). But it is also followed in its adverbial use by many other phrases headed by prepositions with spatial or other non-temporal senses such as "into", "opposite", "in line with", "in front of", "against", "next to", "onto", "over", "on top of". It is also occasionally followed by adverbs. To convince yourself you would probably need to avail yourself of the BNC. DCDuringTALK 18:41, 22 August 2011 (UTC)
Um, are you sure? It seems largely NISoP to me as an adjective. See ["on" at MWOnline]. Our [[on#Adjective]] seems quite lame and inadequate.
"Bang on" seems to me mostly just more emotion-laden and unusual than other adverb-"on" collocations and so is more likely to be remembered. I suppose that such considerations are potentially relevant to inclusion, but they are not part of WT:CFI. DCDuringTALK 14:58, 24 August 2011 (UTC)
I don't think on has a sense to fit the Las Vegas citation, where would seem to mean "appropriate" or "fitting." If you can demonstrate such a sense (apart from this collocation), I will defer. — Pingkudimmi 03:11, 25 August 2011 (UTC)
I think that is exactly the sense in the collocation "just not on". I'll be looking for it. DCDuringTALK 03:36, 25 August 2011 (UTC)
Isn't that the same sense as in "spot on"? —RuakhTALK 03:49, 25 August 2011 (UTC)
By Jove, another bang-on contribution from Ruakh.
In "spot on" and "bang on", the sense seems the same. In "right on", the sense of on may be virtually identical, but my experience with the 60s and 70s usage makes the whole seem idiomatic. In each of these the stress seems to be on the first word of the expression. In "not on" the stress seems equal on each. I think that is a feature of collocations of "not" rather than evidence of some distinction of sense. All four seem related to the idea of "on target", "on point".