rue, be sad, sigh, lament
慨 centers on a heavy emotional response to regret or loss: feeling rueful, sad, or moved to sigh and lament.
慨 combines the heart radical 忄 with 既, which likely contributes the sound and carries a sense of completion or already-having-happened, fitting the idea of looking back with regret.
The heart radical 忄 beside 既 (already) suggests a heart already heavy with past events: rue, sadness, and sighs come from that emotional weight.
For ガイ, imagine a guy sighing with regret: guy -> ガイ, and his heavy heart makes him lament.
indignation; resentment
deeply emotive; moving
deep emotion; strong feelings
indignant lamentation over the evils of the times
indignant lamentation over the evils of the times
one's heart is filled with even deeper emotion; feeling the emotion all the more deeply
deep emotion; being filled with emotion
to regret; to deplore
deploring the course of public events
worrying about the conditions of the country out of sheer patriotism
deploring; lamentation; regret; complaint
indignant; sorrowful
righteous indignation; patriotic lamentation; deploration
worrying about the conditions of the country out of sheer patriotism