beside oneself with joy; in raptures; ecstatic
A yojijukugo describing a state of extreme joy or elation, often used in literary or emphatic contexts.
He was beside himself with joy at the news of passing.
有頂天 is a more common word with a similar meaning of ecstasy or being overjoyed, but 有頂天外 is a rarer, more emphatic yojijukugo variant.
A yojijukugo combining 有頂天 (ecstasy, the highest heaven in Buddhism) with 外 (outside, beyond), literally 'beyond the highest heaven', emphasizing an extreme state of joy.