@Murkrow Yes but this isn't a "word" per se, it's in an idiom, so you'll probably never meet it again, it's not part of Duolingo's database (the one you can check here:
https://www.duolingo.com/words ), so they couldn't use hover thing for it... Instead, they decided to translate the beginning that's not really part of the phrase anyway, and leave it at that.

BTW, the literal translation of that phrase is "he can't reach up to your ankle". I like that image: he's so small and insignificant, he's not tall enough to reach even your ankles... :p