This is the 8433rd most frequent Japanese word.
愛せ
"愛せ" means "love" (imperative form).
The word "愛せる" is derived from "愛する", meaning "to love", conjugated to indicate potential or ability.
彼を愛せるかどうか、心の中で問い掛けた。
I asked myself in my heart whether I could love him.
Here, "愛せない" represents the negative potential form of "愛する", meaning "cannot love".
彼女が愛せないものは何もない。
There is nothing that she cannot love.
"愛せ" appears in imperative form as a command to love.