Compare similar form evolution in Dutch lente (Middle Dutch lentin), German Lenz (Old High German lengizin) "spring." But the Church sense is peculiar to English. The -en in Lenten (n.) was perhaps mistaken for an affix.
"season following winter, first of the four seasons of the year; the season in which plants begin to rise," by 1540s, short for spring of the year (1520s), a special sense of an otherwise now-archaic spring (n.) "act or time of springing or appearing; the first appearance; the beginning, birth, rise, or origin" of anything (see spring v., and compare spring (n.2), spring (n.3)). The earliest form seems to have been springing time (late 14c.).
The notion is of the "spring of the year," when plants begin to rise and trees to bud (as in spring of the leaf, 1520s). The Middle English noun also was used of sunrise, the waxing of the moon, rising tides, sprouting of the beard or pubic hair, etc.; compare 14c. spring of dai "sunrise," spring of mone "moonrise." Late Old English spring meant "carbuncle, pustule."
It replaced Old English lencten (see Lent) as the word for the vernal season. Other Germanic languages tend to take words for "fore" or "early" as their roots for the season name (Danish voraar, Dutch voorjaar, literally "fore-year;" German Frühling, from Middle High German vrueje "early"). In 15c. English, the season also was prime-temps, after Old French prin tans, tamps prim (French printemps, which replaced primevère 16c. as the common word for spring), from Latin tempus primum, literally "first time, first season."
Spring fever is from 1843 as "surge of romantic feelings;" earlier of a type of disease or head-cold prevalent in certain places in spring; Old English had lenctenadle. First record of spring cleaning in the domestic sense is by 1843 (in ancient Persia, the first month, corresponding to March-April, was Adukanaiša, which apparently means "Irrigation-Canal-Cleaning Month;" Kent, p.167). Spring chicken "small roasting chicken" (usually 11 to 14 weeks) is recorded from 1780; transferred sense of "young person" first recorded 1906. Baseball spring training attested by 1889, earlier of militias, etc.
"to grant (immovable property) as security for money lent or contracted to be paid," late 15c., morgagen, from mortgage (n.). Related: Mortgaged; mortgaging.
"motherly care," 1868, verbal noun from mother (v.). Earlier it was used in reference to the rural custom of visiting one's parents with presents on Mid-Lent Sunday (1640s).
"Shrove Tuesday, last day of carnival, day of eating and merrymaking before the fasting season of Lent," 1690s, French, literally "fat Tuesday," from mardi "Tuesday" (12c. in Old French, from Latin Martis diem "day of the planet Mars;" see Tuesday) + gras "fat," from Latin crassus, "thick," which is of unknown origin.
The Norse word also is cognate with Old English læn "gift," which according to OED did not survive into Middle English, but its derived verb lænan is the source of lend (v.). From early 15c. as "a contribution to public finances" (ostensibly voluntary but often coerced; sometimes repaid, sometimes not). As a verb, loan is attested from 1540s, perhaps earlier, and formerly was current, but it has now been supplanted in England by lend, though it survives in American English. Slang loan shark first attested 1900 (see shark (n.)).
also figgey, 1540s "sweet" (as figs are), from fig (n.1) + -y (2). From 1846 (in a book of Cornish words) as "full of figs or raisins." The figgy pudding of the Christmas carol is a dish of dried figs stewed in wine that dates back to the Middle Ages but was more often associated with Lent than Christmas.