1) Part of the ancient practice to have cattle, horses or sheep use different pasture grounds at different times of the year.
1349 ‘from summer agistment in Erringden Park’, Sowerby, and the verbs ‘to winter’ and ‘to summer’ were used in this context: 1598 the horses and beastes of ... Fountance Abbey were kepte on the same pasture in sommer tyme from about May Day unto Mychaelmas beinge ... an highe moorishe and mossy grounde fit onely for someringe and not for wynteringe of any cattel
1634 Wee lay in paine that noe man dwellinge within the ... Lordshipp shall winter any Cattal in any other Lordshipp and bringe them to be ... somered upon the mores, Meltham. The practice was responsible for a number of minor place-names: 1577 my lease of Somerlodge in Swadaile, Easby
1608-9 Somerboothlee ... Wynterboothlee, Warley
1634 ‘John Dyson holds a close of arable and meadow in Meltham called Somerhey’.
2) A summer was a horizontal bearing beam and its use is implicit in Latin documents.
1335 Ad hoc lignea summaria interlacia ac omnia alia genera meremiorum, York. Later we have: 1589 for 33 sommers and 30 planckes, How Bridge
1682 the summers to be eight yeards long, fifteen inches and twelve in gage, Scriven. Summer-tree has the same meaning and is on record from the eighteenth century: 1733 roofe cast, goists and summer trees, Wakefield
1788 sumertrees, beams, reafters, sidtrees, bindings, spars, planks, Meltham. Sommertree Bridge was the name of a bridge in Pickering in 1633.
3) A pack-horse.
1350 jeo devise a Roger mon chambreleyn xx lvyres [sic] et le melior robe que j’ay et le melior somer, Ayton
1400 De xvjs rec. pro j equo vocato somer coquinć, Richmond
1617 and vnto Mr Brigges my parson a summer nagge, Hinderwell.