कर्ता of 7.2.115 अचो ञ्णिति
संधि विच्छेद : अचः णित् ञित्
अनु वृत्ती : वृद्धि अङ्गस्य
Language Meaning: at णित् ञित्, of अचः, of अङ्ग, वृद्धि
Literal Meaning
At push inward that and at surface (hyde/cloth/net); of what goes outward; of स्वर; do वृद्धि
Commentary
Why अच and not अक ? There is no वृद्धि possible for अ ओ ऐ औ in any case?
अच also refers to repetition. Repetition causes वृद्धि to be conveyed.