The word is not attested otherwise and lacks an etymological explanation.
s.
1punctus, dot in punctuation, placed at the centre-point of letters, not on the line:
(
1485-1509
)
Mailes de William primers ové lettres en ceste manere ‘COMA’ [...] secunde manere ‘COM.A’ et la varance est le tule entre lez M et A […]
E163/9/21
tule1 (1485-1509)