Why is Christian Lent called Lent?

Roman Catholic AnswerLent is the English name for Quadragesmia, which is the forty days from Ash Wednesday to Holy Saturday (excluding Sundays) observed as a preparation for the passion, death, and resurrection of our Blessed Lord, and as a time of penitence, prayer, and fasting, spiritual and physical. It is from the Old English Word, lencten, which means the "spring season".

from A Catholic Dictionary, edited by Donald Attwater, Second edition, revised 1957