अत्

अतँ = अ त चंद्र बिंदी

धातु अर्थ
at सातत्यगमन = सातत्य = सतत + ष्यञ् + गम् ल्युट्
aligned inside tumbi pull inside stone tumbi + moving/Live fish subjugate(d) inside

रूढ अर्थ
move steadily = This is misintterpretation from later day meanings of सतत and गमन but it stuck because it is inline with here+float