xī
(particle in old Chinese similar to 啊)
This is a grammatical particle — its meaning comes from how it's used in sentences, not from its components.
脏兮兮
zāng xī xī
dirty
兮兮
xī xī
(particle used to exaggerate certain adjectives, in particular 神經兮兮|神经兮兮, 髒兮兮|脏兮兮, 可憐兮兮|可怜兮兮, and 慘兮兮|惨兮兮)
可怜兮兮
kě lián xī xī
miserable