The place name Glasgow derives from a Gaelic description of a green place on the banks of the river Clyde. In Older Scots this was variously written as Glasgu, Glasgow and even Glaskow. In the older language u, v, and w were interchangeable and so these spellings show that the pronunciation was Glas-koo which is close to the original Gaelic. By the 17th and 18th centuries a Scots form Glesca (or even, Glesga) - had begun to emerge which follows an established rule in Scots whereby ou/ow offen becomes ca(e) in speech, such as with Lithca(e) (Linlithgow) or Embra(e) (Edinburgh or Edinburrow). This means that the English version Glasgow (glas-go) is an incorrect pronunciation.

Glasgow was a cathedral city from the 12th century onwards and the Scots language became the ordinary language of the town that grew up around the religious community. Glasgow was no exception to the growth of written Scots in the 14th and early 15th centuries. Already, in 1424, a dispute between the burghs of Dumbarton and Renfrew was conducted through Scots as was a document issued by the laird of Kilbride to the laird of Ardrossan in 1421, concerning lands in Lanarkshire. The earliest surviving document in Scots that comes from Glasgow itself is a contract between Prior Oswald of the Friars of Glasgow and John Fleming of the Couglen, dated 22 January 1433/4. In this document it is stated that:

the said Johne has set in to feferm tyll the said Priour and the Convent, or quha sa be Priour in that Convent, a rud of lands lyand on the gat at setkis fra the Markat Cors tyll the he kyrk Glasguthe said priour and convent payit thar for yherly tyll the said Johne his ayris or assignyis ten schylling of vsuale mone o the kynryk of Scotlandand stabylling for twa hors in that samyn place or ellis within the Freris tyll the said John Flemyn qwhen him lykis tyll cum tyll do hys erandis or mak residens within the toun

Not long after this period other transactions were being carried out in Scots in and around Glasgow and the local council also began keeping records in the language that the councillors spoke. Take, by way of example, a decree of the burgh court, 6 July 1581, on the subject of the Glasgow fair:

The quhilk day, the peace of the fair wes proclamit be David Coittis, mair of fee, vpone the Greyne, and be Richarde Tod, toun officiare, vpone the croce, efter the forme and tenoure vnderwrittin: Forsamekle, as this day is the sext day of Julii, quhilk is the fair evin of Glasgow, and the morne the fair day, quhilk fair continewis the space of aucht dayis, thairfore I inhibit and forbiddis straitlie in our Souerane Lordis name and in name and behaulfe of ane noble and potent lord Esme erle of Lennox, lord Darnlie and Obinze, etc, prouest, and baillie of the baronie, and in name of the baillies of this toun, that nane of our Souerane Lordis legis cumand to this fair, repairing thairin, gangand thairfra do ony hurt or trublense ane to ane vther for auld dett or new dett, auld feid or new feid, bot leif peceablie and vse thair merchandice and eschange vnder Goddis pece and our Souerane lordis protectioun, vnder all hiest pane and charge that may be impvt to thame doand in the contrare, and to be callit and accusit for breking the Kingis Maiesteis pece and trublance of his hienes mercatt.

To a modern day Glaswegian the documents above will seem both familiar because of the Scots still spoken today and unfamiliar because of the words that have changed, or because Glaswegians are not taught to write in the language they speak. Yet in this earlier period speaking and writing in Scots was entirely natural because the people who ruled Scotland also spoke the language. After 1603, when James VI also became king of England, the royal court moved to England, but Scotland was still self-governing and Scots remained the language of formality and business until the Union of 1707. In February 1652, for instance, Glasgow council minutes record the election of commissioners:

The burgesses and neichbouris of this brugh being conveaned for electing of ane commissionar to the meitting appoynted to be haldane at Dalkeith the saxteine of this instant, Mr John Spreule, clerk, was electit preces of the said meitting, and efter advyce takine it was thocht guid twa commissionars sould be chosine, bot they to conclude nothing quhill the towne got tymeous adverteisment quhat was requyred

Slowly the written language became more Anglicised (such as nothing rather than na(e)thing in the text above), but clearly the language of Glaswegians which was closely related to other Scots-speaking areas was still in official use. Another example of the language, from 1670, is the decree which was issued by the council against orray wemen who were branded as loose-living by the council whose members

have concluded that twa of their number sall goe throw with the minister ilk quarterthe hail quarter and ilk particular hous thereof, and to tak notice of ilk idle and orray woman that hes takin wp houssis, and to mak them aether presently to returne to service or then act and obleis themselfes to remove aff the toune

In the above extracts, spellings such as towne and hous(s) were pronounced as toon and hoose as they are today while orray is a form of the Scots orra which has the basic meanings of spare or unattached or odd. And in this period the Scots language was the usual medium of instruction in schools. For example, in August 1660, the burgh council of Glasgow allowed James Corss, a maths teacher, and himself a native of Glasgow to take wp ane schoole heir for teaching of theis artes and sciences in the vulgar native tongue. In those days vulgar simply meant the daily non-Latin language. We can also see in the records those pronunciations an turns of phrase which are today closely associated with more modern speech. For example in 1688 the council declared a proclamation to be sent through the toune for keeping the morrow, which would now be rendered as the morra.