मन्

मनँ = म न चंद्र बिंदी optional उ
inside pull (optional उ as स्वर विभक्ति making this क्रियापद)
inside pull (high tide) outward surface

explanation of धातु पाठ अर्थ
ज्ञान = physical sense - widen net upto = fish pull; मारण तोषण
ज्ञान = upto wide surface, in sense of knowing terrain = inside pull

रूढ अर्थ
mind, know, understand, contemplate from the abstraction of pull inside

commentary
Inside is in the context of the water surface - tide.