malpli

Malpli is simply pli with the reversing prefix, and the whole comparative system follows the same logic: pli and malpli, plej and malplej. The thing compared against takes ol, and a quantity takes da, so malpli da tempo but malpli interesa ol tio. English speakers agonise over "less" versus "fewer" and Esperanto simply does not have that argument - malpli da homoj and malpli da akvo are both correct. In practice speakers often turn the sentence round and use pli on the other item, which reads more lightly.