• 講演こうえん — lecture / public speech
• 講義こうぎ — academic lecture
• 講師こうし — instructor
• 講座こうざ — course (series of lectures)
• 講習こうしゅう — training course
• 講談こうだん — traditional storytelling
• 休講きゅうこう — cancelled lecture
• 受講じゅこう — attending a lecture / taking a course
• 補講ほこう — supplementary lecture / makeup class

講 combines the 言 (speech / language) radical with 光 as the phonetic element. It originally referred to gatherings for teaching or explaining doctrines. Today it broadly means lectures, explanations, and organized instruction.

先生せんせいの 講義こうぎは とても分わかりやすかった。
The teacher’s lecture was very easy to understand.

来週らいしゅう、有名ゆうめいな 講演こうえんが 行おこなわれます。
A famous lecture will be held next week.