प्रभौ परिवृढः

The irregularly formed परिवृढ means 'Lord'.
This is formed, like दृढ, from वृह् or वृंह् ॥ When not having the sense of 'Lord', we have परिवृहितम् and परिवृंहितम् ॥

The ह is elided first as an anomaly. By so doing we can get the forms like परिव्रढयति, परिव्रढय्यगतः; पारिवृढीकन्या ॥ The form परिव्रढय्य is formed by ल्यप् instead of ktva ॥ Though the full noun is परिवृढ and णिच् is added to such a noun, yet for the purposes of ktva it is considered as a compound verb, having परि as upasarga. In fact, णिच् is added to वृढ, and the root becomes व्रढि, and then ktva is added to this root, and then there is compounding of परि with this word ending in ktva, and then by the regular process the ktva is replaced by ल्यप् ॥ The general rule is that Derivative roots formed from nouns, like परिवृढ, उत्मनस्, सुमनस् &c which have an upasarga as one of their formative elements, are treated as if they were compound verbs having those upasargas. The result of this is, that though the full noun is सुमनस्, yet in the derivative verb, सु will be treated as an upasarga, as in ordinary compound verbs. Thus the augment अ in the Imperfect is added after सु and not before it, as स्वमनायत, उदमनायत ॥ The rule is उपसर्गसमानाकारं पूर्वपदं धातुसंज्ञाप्रयोजके प्रत्यये चिकीर्षिते पृथक् क्रियते ॥ The Participial form of these words is therefore with ल्यप् and not क्त्वा, as सुमनाय्य and उन्मनाय्य ॥ The only exception to this rule is the noun संग्राम, in which the upasarga सम् is not considered as a separate member in the Derivative verb. This being the general rule, in परिव्रढयति the portion परि is treated as an upasarga, and व्रढयति as the verb, and its accent is governed by तिङ्ङ तिङ् 8.1.28 i. e. it becomes altogether unaccented and परि retains its accent. So also परिव्रढय्य, where is परि is compounded with the Participial form व्रढित्वा, and then त्वा is changed to ल्यप् by 7.1.37.