recitation, poem, song, composing
咏 centers on giving voice to words in a rhythmic or artistic way: reciting, composing poems or songs, and the act of vocal expression itself.
咏 combines 口 (mouth) with 永, which likely contributes the sound and may suggest a drawn-out vocalization. The character is a variant form of 詠, where 言 (speech) is replaced by 口.
A mouth 口 producing a long, flowing sound like the shape of 永: reciting a poem or song.
For エイ, imagine an 'A'-list poet reciting an epic poem: 'A' -> エイ, and the mouth 口 shapes the words.