LentyoudaoicibaDictYouDict[Lent 词源字典]
Lent: [OE] The etymological meaning of Lent is ‘long days’. It comes from *langgitīnaz, a prehistoric West Germanic compound formed from *lanngaz ‘long’ and an element *tīnadenoting ‘day’. This signified originally ‘spring’, an allusion to the lengthening days at that time of year. It passed into Old English as lencten, which became Middle English lenten, but in the 13th century the -en was dropped from the noun, leaving Lenten to function as an adjective. By this time too the secular sense ‘spring’ was fast dying out, having been usurped by the application of Lent to the period between Ash Wednesday and Easter.
=> long[Lent etymology, Lent origin, 英语词源]
Lent (n.)youdaoicibaDictYouDict
late 14c., short for Lenten (n.) "forty days before Easter" (early 12c.), from Old English lencten "springtime, spring," the season, also "the fast of Lent," from West Germanic *langa-tinaz "long-days" (cognate with Old Saxon lentin, Middle Dutch lenten, Old High German lengizin manoth), from *lanngaz (root of Old English lang "long;" see long (adj.)) + *tina-, a root meaning "day" (compare Gothic sin-teins "daily"), cognate with Old Church Slavonic dini, Lithuanian diena, Latin dies "day" (see diurnal).

the compound probably refers to the increasing daylight. Compare similar form evolution in Dutch lente (Middle Dutch lentin), German Lenz (Old High German lengizin) "spring." Church sense of "period between Ash Wednesday and Easter" is peculiar to English.