most of all; extremely; supremely
Adverbial phrase meaning 'to the highest degree', used to emphasize adjectives or verbs. Often interchangeable with この上もなく.
I am supremely happy.
He is an extremely kind person.
Standard kanji-kana spelling.
Variant using the kanji 無 for なく; less common but still seen.
From この上 (kono ue, 'beyond this') + なく (naku, adverbial form of ない 'not'), literally 'there being nothing beyond this'.