This is the 46th most frequent Japanese word.
開か
"開か" (hiraka) is the stem form of the verb "開く" (hiraku), meaning "to open" or "to be opened."
Here, '開か' is used as a verb in its negative potential form implying the door cannot be opened.
ドアが開かないように鍵を掛けました。
I locked the door so it wouldn't open.
Here, '開か' is part of the verb '開かれる', meaning 'to be opened', suggesting a meeting or forum is being convened.
そのテーマについて自由に意見交換する場が開かれた。
A place for freely exchanging opinions on that theme was opened.
Here, '開か' is part of the adjective '開かれた', which metaphorically means being open, as in open-minded or progressive.