smaller is nitxiapi

nitxiapi = smaller (adjective) (some things Google found for "nitxiapi": an unique term; did not match any documents; somewhat similar Battle of Xiapi was fought in China in the winter of 198 towards the end of the Han Dynasty)

Word derivation for "smaller" :
Basque = txikiago, Finnish = pienempi
Miresua = nitxiapi

For good measure, I decided, to post smaller too. Small is nitxi. The comparative adjective suffix in Miresua is -api.

Alice got uncomfortably large in the White Rabbit's house: "If I eat one of these cakes," she thought, "it's sure to make SOME change in my size; and as it can't possibly make me larger, it must make me smaller, I suppose."

larger is hurdiapi

hurdiapi = larger (adjective) (some things Google found for "hurdiapi": an unique term; search did not match any documents)

Word derivation for "larger" :
Basque = handiago, Finnish = suurempi
Miresua = hurdiapo

Larger is a comparative adjective. So, I'm getting into some grammar here.

In Basque, the comparative is formed by adding -ago. In Finnish, the comparative adjective is formed by adding -mpi. (Apparently there can be vowel changes too). I decided to make the suffix for the comparative adjective in Miresua be -api.

An adjective in Miresua will be inflected, at a minimum, to agree with the noun it modifies as far as being singular or plural. Miresua plurals are formed by adding -t or -at.

In Alice's Adventures in Wonderland, Alice grows larger and smaller.