苦 (Kanji for suffer)

Onyomi

KU	as in, 'My KUCHI ( 口 ) was suffering from too much candy. '

The old flower was suffering : wilting, turning brown, being eaten by aphids.

にが*い	bitter taste ー medicine, okra. Can also be used figuratively - the bitter taste of defeat. ★★★☆☆
( が ) くる＊しい	adjective describing mental suffering - which is caused BY 痛み　(physical pain). i.e. 'My throat is 痛い、 so talking or swallowing is 苦しい’ ★★★☆☆
( ｘｘｘに ) くる＊しむ	to hurt or suffer　from XXX ★★★☆☆

苦労(くろう)

hardships ★★★☆☆
苦 (suffer) + 労 (labor) = 苦労 (hardships)

xxxは苦手(にがて)

this is not my thing! ★★★☆☆ KUNKUN
苦 (suffer) + 手 (hand) = 苦手 (this is not my thing!)

this has 2 meanings. One is "I'm not good at this" and the second is "I don't like this" Clever Japanese!

苦情(くじょう)

a grievance or complaint ☆☆☆☆☆
苦 (suffer) + 情 (emotion) = 苦情 (a grievance or complaint )