become tired, work busily
劬 centers on physical or mental exhaustion from sustained effort: becoming tired through busy work or overexertion.
劬 combines 句 (which may contribute a sound element) with 力 (strength/effort), suggesting the idea of exerting effort to the point of fatigue.
The left side 句 looks like a bent-over figure, and the right side 力 is strength. Picture someone using all their strength until they are bent over and tired from working busily.
For ク, imagine working so hard you feel like you're in a long queue that never ends: queue -> ク, and the endless waiting makes you tired.