Compare the two cases:
• Mushtarak - عَيْنٌ: the same word was established separately for several meanings such as eye and spring. A contextual clue identifies the intended meaning.
• Technical Shariah assignment - الصَّلَاةُ: in ordinary language Salah was used for supplication; the Shariah assigned it to the known act of prayer as a technical meaning.
The source therefore does not call Salah Mushtarak merely because both a linguistic and a Shariah usage can be mentioned. Two usages alone do not prove the multiple original assignment required by the definition.