The name Mo Laisse is a hypocorism (or devotional nick-name) from the name Laissrén, and that name itself derives ultimately from Old Gaelic lasar ‘flame’. There are literally dozens of apparent saints with this name in Gaelic sources – though most of them are probably erroneous duplications of one or other of the two best-known saints of this name, Mo Laisse of Leighlin and Mo Laisse of Devenish.
It is likely that one of these saints called Mo Laisse is commemorated in the medieval church of Strachur, whose name first appears in the sixteenth century as Kilmalash. In later forms (including that of the modern Ordnance Survey map) a g appears in the name, giving Kilmaglash and similar forms. But although there are traces of saints called Glais and Glaisne, which could have resulted in a hypocorism like Mo Ghlais, it is more likely that Mo Laisse is the saint commemorated here. For one thing, the cults of Laisrén or Mo Laisse are very well attested and evidently more popular in the Middle Ages. In addition, a saint called Mo Laisse is commemorated elsewhere in this area in Lamlash (Eilean Mo Laisse, ‘Mo Laisse’s island’) by Arran, and possibly in Ardmoleish in the nearby Isle of Bute. And thirdly, because Mo Laisse’s medieval profile includes various a story connecting him to St Munnu whose cult is also very important in the area around Strachur and who was also associated in his Life with Devenish, the monastery of Mo Laisse. As geographical associations between two saints’ cults are often reflected in stories connecting those two saints, we may give more weight to the claim of Mo Laisse to be the patron of Kilmalash.
There is a medieval ‘Life of St Laissrén alias Mo Laisse, abbot of Leighlin’ (Vita Sancti Lasrani seu Molaisse Abbatis de Lethglenn) in which St Munnu makes a brief appearance when Mo Laisse’s mother sends her boy to study with St Munnu in Scotia (Scotland north of the Clyde). In the same Life this Mo Laisse ‘sought a certain island inter Britanniam et Scociam‘ (by which the author probably meant ‘between a British- or Old Welsh-speaking area and Scotland’), and this may well refer to Arran, where Lamlash commemorates a St Mo Laisse. The same Life also says that Mo Laisse of Leighlin was the nephew of St Blane, whose foundation was on the Isle of Bute, close to Arran and not very far from Strachur. These fragments of evidence lend tentative support to the idea that this Mo Laisse was commemorated at Kilmalash, but this is far from certain. His feast was on 12th September, and he is commemorated thus in the ninth-century ‘Martyrology of Óengus':
‘the feast of Laissrén the beautiful,
from multitudinous Devenish.’
Without further evidence of medieval devotion to a saint at Strachur – perhaps a saint’s feast being marked in some way, or a Latin record of the dedication of the church – we cannot be certain who in fact was commemorated.