yè sí pron /jè sí/
Definitions
  1. who, whom, whose interrogative
    Yè só o rí Who did you see?
Etymology
From yè + sí. Compare with forms in other Yoruba dialects, Ondo è sí, Ekiti ì sí, Egba & Ijebu lè sí, Iyagba nè ghí. The use of "sí" can be seen in many interrogative forms in the respective dialects. Cognate with Itsekiri nè sín, Olukumi è ghí, Ede Ije lè é.
Component words
Source: Wiktionary, where this word is spelled “ye si”. Reference: en-ye_si-yo-pron-PHNbHs0w