I have no idea, whether someone already covered it or not, so I'll make a small post on it. I'm used to pronounce her name as Ai-kra, not Ee-kra, but no matter.
I wonder, why Aku chose exactly this name for his female form, what meaning could be behind it. I mean, ikra or ikura is literally a roe of salmon (salmon caviar), so I don't know, what could make Aku to choose exactly this name. Maybe because in certain cultures it's a symbol of prosperity, high status, richness and transformation. And from what I know, Japanese kinda very like ikura, but don't eat raw salmons, 'cause they're dangerous due to lots of parasites in them.
So, I assume Aku made the name Ikra as amalgamation of Japanese words iku and kuro/kura. Kura or Kuro can mean "treasure" (or something, what keeps treasures inside), "dark" and "black", Iku can mean "come/go to something/forward", so in this case Ikra means "Coming/arriving darkness", what can be viewed as a mockery, warning and foreshadowing for Jack.
Although I like variations "sensual/ardent dark", if you understand, what I mean, giving the context of the episode and Ikra's backstory's parallel with Jack's, and also "dark treasure", because Aku is obviously and without any doubts a dark treasure.
Or maybe the answer is simple — Ikra is just an anagram and a reference to Akiro the wizard from Conan the Barbarian, played by Mako, Aku's voice actor.