Noun, Suru verb, Intransitive verb
taking great pains
Yojijukugo (four character compound)
苦心惨憺の末、考え出した企画が、会議で一瞬にして却下されちゃうんだからな。After all the trouble we went to in coming up with that project, it only took them a second to shoot it down in the meeting.
Also written 苦心惨澹【くしんさんたん】