Thirlage was a feudal servitude (or astriction) under Scots law restricting manorial tenants in the milling of their grain for personal or other uses.

The term thirlage is a metathesis of Scots thrillage 'thralldom', derived from thril 'thrall', which was a body servant, retainer, or vassal to a noble or chief.

[5] Thirlage was the feudal law by which the laird (superior) could force all those vassals living on his lands to bring their grain to his mill to be ground.

Multure (or mulcture), pronounced 'mooter', was the name for the mill toll: a fixed proportion of the tenant's grain, paid to the miller by the suckener to grind the corn.

Aiton records in 1811 that barley, wheat, peas, beans, and every form of green crop were exempt from multure.

Early Scottish multurers' duty to use their baron's mill could be legally enforced by the miller breaking quern-stones.

[13][12] The Act allowed those suckeners bound by thirlage to make a one-off payment that 'bought' them out of the various legal requirements: And whereas there is a kind of thirlage known in the law and practice of Scotland, called a thirlage of the invecta et illata, to which sundry towns, burghs, burghs of barony, villages or other places in that part of the kingdom and the inhabitants thereof are subject, which thirlage it is expedient to allow to be purchased by the persons subject to the same: Be it therefore enacted, that if any inhabitant or inhabitants of such town, burgh, village or place, shall be desirous to purchase an exemption from the said servitude of thirlage, and all and every the services and prestations incident thereto, to which the whole town, burgh, village or place is liable, from the proprietor of such mill or mills entitled to the same, it shall be lawful and competent to them to apply in manner above mentioned to the sheriff or steward depute of the county in which such town, burgh, village or place is situate, who shall take such proceedings and summon a jury in such manner as is herein-before particularly directed, which jury shall by their verdict fix and determine the full value in money of such right of thirlage in perpetuity; on which verdict and determination the said sheriff or steward depute or substitute shall pronounce decreet against the person or persons so petitioning or applying to him as aforesaid for the sum so fixed and determined by such jury; on payment of which to the proprietor of the mill, such town, burgh, village or place, or such inhabitant or inhabitants thereof, formerly subject to such thirlage, shall thenceforth be for ever freed and relieved from the same.Section 55 of the Abolition of Feudal Tenure etc.

The width of some of the first roads was determined by the requirement to have at least two people on either side of a new grindstone being transported, with a wooden axle called a 'mill-wand' passed through the hole in the centre.

[14] Suckeners would place a small amount of grain in a bag at the mill which would be used to help feed the poor or those suffering hard times.