Reduplication
Reduplication is repeating a word (near)-exactly to form a new word or phrase. In English, it occurs in words like "bye-bye" and "zigzag", in contrastive focus reduplication, and with "schm-".
Reduplication has often been suggested for Toki Pona, generally as an intensifier (for example, suwi suwi for "really cute"). However, it is not widely used, with a, mute, and suli being used for emphasis instead.
A potential ambiguity of this feature would be the phrase lili lili. Under current standard grammar, it means "a little small". If read as reduplicated, it would also mean "very small", becoming an auto-antonym.