The word "Ṣalāh" is one of the most significant Quranic terms, having long engaged exegetes, jurists, and Quranic scholars. In pre-Islamic Arabic, it signified "supplication" and "attentiveness." However, with the revelation of the Quran and the establishment of Islamic law, it underwent a profound semantic shift, becoming a core pillar of Islam. This study, using a descriptive-analytical approach and focusing on verse 110 of Sūrah al-Isrā', investigates this semantic transformation. The findings reveal that "Ṣalāh" in the Quran carries multiple meanings, including ritual prayer, supplication, obedience, adherence, and compassionate regard. In verse 110 of al-Isrā', it specifically denotes ritual prayer with recitation, and the verse instructs believers to moderate between loud and silent recitation. Linguistic, exegetical, hadith, and jurisprudential evidence confirms that here, "Ṣalāh" bears its specific legal sense (ritual prayer), which aligns perfectly with the surrounding context. The study further demonstrates that the term evolved from a general meaning (supplication) to a distinct legal one (ritual prayer with defined pillars and conditions)—a change rooted in the legislative process and the institutionalization of worship in Islam. Additionally, the narratives of the Infallibles played a crucial role in cementing this legal meaning. The verse also holds significant weight in deriving jurisprudential rulings on loud versus silent recitation. Overall, this research highlights the dynamic nature of Quranic vocabulary and the intricate relationship between language, revelation, and legal development.