exaggerate
躛 centers on exaggeration, especially in speech or description. It is a rare kanji with a narrow meaning.
The exact historical development of 躛 is uncertain. It appears to combine 足 (foot) with a phonetic component, but the origin of the top part is unclear.
The top part looks like a complex, overblown structure, and the bottom 足 (foot) suggests stepping beyond the truth. Together they picture exaggeration as an overblown step.
For エイ, imagine an exaggerated 'A' grade on a test: 'A' -> エイ, and the kanji's meaning of exaggeration fits the over-the-top grade.