दीर्घ

दीर्घ = दृ + घञ्
objectify(दृ)
OR
दीर्घ = द इ र घ
roll inward flow hunt = hunting inside rolling wave/water = deep (level 2)

commentary
Compare with ह्रस्व and प्लुत
ह्रस्व =low depth, subsequently identified as depth of one मात्रा - एक वचन
दीर्घ = deeper but leg is yet connected to sand. subsequently identified as depth of two मात्रा - द्वि वचन
प्लुत = afloat subsequently identified as depth of many मात्रा - बहु वचन

रूढ अर्थ

1. long
2. saal tree
3. long vowel