a combining form with the meanings “very large in comparison with others of its kind” (maxi-budget; maxi-taxi); “of great scope or intensity” (maxi-devaluation; maxi-service); (of clothing) “long, nearly ankle-length” (maxicoat; maxiskirt).
Origin of maxi-
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
word-forming element meaning "maximum, very large, very long," from comb. form of maximum.
Online Etymology Dictionary, © 2010 Douglas Harper