A question about the origin and meaning of 'hours on end'

Question

We sat and waited in the emergency room for hours on end.

Idioms - The Free Dictionary

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The Ngram demonstrates that the frequency of usage of the saying is hours, then days, then months, lastly years - which might have been expected.

Quora, in answer to the question of origin states :

The idiomatic "on end" -- meaning consecutively, without intermission -- dates back to 1634, according to the Oxford English Dictionary.

But that is not quite correct, for the 1634 reference is not about time at all.

1634 S. Rutherford Lett. (1863) I. xxxii. 111 And was brought, thrice on end, in remembrance of you in my prayer to God.

OED

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The first quote I can find that is relevant is just four lines below the 1634 one :

1882 W. Besant All Sorts of Men I. vii. 184 Working sixteen hours on end at twopence an hour.

But what does it actually mean ? Is the concept viewing time like a ladder, up-ended, so that we look at the stretchers of the ladder (one above the other) like hour-long slats heaped up ?

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[EDIT :]

I wonder if 'on end' originally came from the expression 'end on end' regarding physical objects laid end against end in a line.

The Ngram for 'end on end' shows that it pre-dates 'on end' by twenty years.

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Answer 1

The OED provides four senses in which on end is used - see (a) - (d) below. The first (a), meaning "at last" has no examples since 1400. The second (b) is the meaning to which you refer in your question. The third (c) does not seem relevant, but (d) which has an entry from 1300, would seem to be the original, upon which today's use is metaphorical.

on end (see also an-end adv.):

†a. at last.

c1175 Lamb. Hom. 25 Al swa he dođ swa þe swica þe bi-swikeđ hine seolfe on-ende.

c1320 Cast. Love 1064 Þat foreward on ende wel was i-holde.

c1400 (▸?c1380) Pearl l. 186 I drede on ende quat schulde byfalle.

b.consecutively, without intermission; also right or straight on end: (a) >consecutively, uninterruptedly;(b) immediately

1634 S. Rutherford Lett. (1863) I. xxxii. 111 And was brought, thrice on end, in remembrance of you in my prayer to God.

1778 Learning at a Loss II. 147 'Twas at his House they [two lovers] broke cover. And then took off strait an End to Edinburgh.

1836 in Byron's Wks. (1846) 552/1 The ministerial prints raved for two months on end.

1837 T. Hook Jack Brag I. i. 16 The fox going away right on-end across a heavy country.

1867 W. H. Smyth & E. Belcher Sailor's Word-bk. Right on end, in a continuous line; as the masts should be.

1882 W. Besant All Sorts of Men I. vii. 184 Working sixteen hours on end at twopence an hour.

1883 S. Baring-Gould John Herring I. xi. 154 I be going to die right on end, I be.

c. on (one's) way, forward, along; (whence to come on end, to come >forward; >(Middle English) to set spell or tale on end, to begin a discourse).

c1340 Cursor M. (Trin.) 1295 Seeth set tale on ende [Cott. spell o-nend] And tolde whi he was sende.

1627 R. Sanderson Ten Serm. 404 These would bee soundly spurred vp, and whipped on end.

1630 R. Sanderson Serm. II. 266 Others will not come on end chearfully.

d. in an upright position, resting on (its) end.

a1300 Cursor Mundi 25049 Þe cros..quen it es sett on end vp euen, It takens pes tuix erth and heuen.

1785 W. Cowper Task iv. 86 Katerfelto, with his hair on end At his own wonders.

1836 Random Recoll. Ho. Lords xvi. 383 His dark hair..stands on end on the fore part of his head.

1839 W. Irving Chron. Wolfert's Roost (1855) 143 A great hotel in Paris is a street set on end.