究
キュウ, ク, きわ.める, きゅ
research, study
JLPT4 G3 S7 F368
As per 九# (bump up against and bend/curve) + 穴 hole → fumble about in the far reaches of a hole in seeking something (compare 探) → *investigate*; *research* (compare 考) → *master* (a discipline). Compare also 奧.
[Full Kanji Etymology List]