Definitive Jest

Entry: matins (n.)

In context:  "But so Blood Sister eventually gets the girl clean, by nurturing her through Withdrawal in a locked sacristy; and the girl becomes less sullen by degrees that have audible clicks to them - the girl stops trying to dicky the lock of the sacramental-wine cabinet, stops farting on purpose during matins and vespers, stops going to the Trappists who hang around the convent and asking them for the time and other sly little things to try to make them slip up and speak aloud, etc."

Definition:  The service, usually consisting of or including the office of matins (sense 1b), preceding the first mass of the day. Now hist. and rare.

1b being:

One of the daily offices appointed in the breviary of the Western Christian Church, usually taken as forming (with the following office, lauds) the first of the canonical hours. Also: an analogous part of certain other minor devotions modelled on the canonical hours; esp. in matins (and hours) of the Blessed Virgin Mary . 

Other: I didn't know of the above sense of matins, but was more familiar with:

 poet. The morning song of birds.

and

 A morning duty or occupation. rare.

The etymology here is halfway-helpful:

Etymology:  < Anglo-Norman and Old French, Middle French, French matines (11th cent.), a specialized sense (after post-classical Latin matutinae (plural): see matutine n.) of the plural of matin morning (10th cent.) < classical Latin mātūtīnum , use as noun (perhaps short for mātūtīnum tempus ) of neuter singular of mātūtīnus belonging to the early morning (see matutine adj.). Compare Spanish matines (1207), maitines (1343), Catalan matines (c1284), Old Occitan matinas (13th–14th cent.); and also Italian mattino (a1313; mid 13th cent. as maitino , maitina ), Spanish matutino (15th cent.). In branch II. either a re-formed singular form inferred from the α forms, or (especially in later use) directly < French matin.

The 16th-cent. form matenses shows analysis of the word as singular with the addition of an analogical plural ending.

SNOOT score:  2
 
Page: 705

Source: Oxford English Dictionary