The law courts of England recognize four terms when the courts are open, constituting together the legal year, for the pleading of legal business: Hilary Term (11th January to Wednesday before Easter*), Easter Term (Tuesday after Low Sunday to Friday before the "spring holiday"†), Trinity Term (2nd Tuesday after the "spring holiday" to 31st July) and Michaelmas Term (1st October to 21st December). Unhappily, in these lawless (or over-legalistic?) days, provision has perforce been made for the courts if need be to sit during vacation time...
It is obvious enough that these terms are so-named after religious feasts: St Hilary's day (to-day, the 14th of January - but in the BCP and the Novus Ordo alike, the 13th); Easter Sunday; Trinity Sunday; and Michaelmas (29th September).
* How apt for the courts to last sit upon Spy Wednesday, as the Irish call it: the day when Judas betrayed Our Lord!† The so-called spring holiday is the bank holiday on the last Monday in May, unless it be transferred to a different date.
Hilarymas, again marked a day early on the 13th, celebrates the end of Christmastide in Sweden - lots of eating, drinking and merriment, and at the end one throws the old Christmas tree out the window!
Dom Guéranger tells that in honour of St Hilary as the Western Athanasius, the triumphant defender of the Nicene Faith, the Church of Poitiers, once his diocese, long sang the Preface of the Trinity on his feast day to signify his entire life and sanctity as centred on the Most Holy Trinity; and Bl Columba Marmion quotes this prayer of St Hilary in worshipful devotion to the Trinity:
Preserve without stain, I entreat Thee, the cult of my faith, and grant that until I sigh my last breath my conscience may bear witness to me; that I, who was baptized in the name of the Father and of the Son and of the Holy Ghost, may forever possess that which I professed in the symbol of my regeneration; Thee, Our Father; that I may adore Thy Son with and as Thyself; that I may receive as mine Thy Holy Spirit Who proceeds from Thee through Thy only Son. Truly, I have a witness worthy of all faith to guarantee my belief, Him Who said: "All things whatsoever the Father hath are Mine," my Lord Jesus Christ, Who dwells in Thee, Who ever God, is of Thee and beside Thee and Who is blessed forever and forever. Amen.