This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
讏 combines 衞 (guard, defend) with 言 (speech). The exact historical development is uncertain, but it likely relates to speech or words associated with guarding or defense.
The top 衞 suggests guarding, and the bottom 言 is speech. Picture guarded or defensive words, but remember the meaning is uncertain.
For エイ, imagine a guard saying 'A!' (エイ) as a warning cry: the guard's speech (言) under the guard component (衞) makes the sound エイ.