August turns into September, so time for a thread of medieval names for what Chaucer calls the 'laste ende' of summer

How about the GREASE TIME (more on this below)? HARVEST, of course, but also the REAPING and RIPING (i.e. ripening) TIME

John Lydgate calls this season the CANICULAR DAYS, the end of the 'dog days' which run from hot summer to leaf fall

LAMMAS TIME, August just gone, is, as Trevisa’s translation of the Polychronicon explains,

’whan the cornes were in feeldes, fruyt on trees, and grapes on the vynes’

GREASE TIME, August and early September, is when the deer are fattest and readiest for hunting:

‘For nowe ys grece-tyme [GREASE TIME] of the yeer
That baruns [barons] bolde schulde hont [hunt] the der [deer]’

(Sir Gawain and the Carl of Carlisle)

Chaucer brings Latin AUTUMNUS/French AUTOMNE into English in his translation of Boethius, helping his readers with a gloss:

‘The leeves that the wynd…hath reft [taken] awey in AUTUMPNE (that is to seie [say], in the laste ende of somer)’

‘The Assembly of Ladies’, a poem perhaps written by a woman around 1475, begins not in clichéd spring (yawn) but with autumn:

'In Septembre, at fallyng of the leef,
The fressh season was altogydre [altogether] done
And of the corn was gadred [gathered] in the sheef…'

And this might be remembered by Stephen Hawes in his Example of Vertu (1504):

'In Septembre in fallynge of the lefe
Whan Phebus made his declynacyon
And all the whete gadred was in the shefe…’

The phrase FALLING/THE FALL OF THE LEAF eventually gives us FALL for autumn in the 16thC

Elizabeth, duchess of Norfolk complains to Cromwell in 1537 about the physical effects of her abusive marriage: she is ill both at ‘the fall of the leaf and at the spring of the year’

Image in first tweet:
The Cotswolds (British Railways poster artwork)
Paul Chater (1878–1949)