noun, noun or participle which takes 'suru'
thinking happily of; cherishing in thought
Rare literary noun or suru-verb meaning to think of something with joy or fondness. Not used in everyday speech; found mainly in older or poetic writing.
古い手紙を読みながら、彼は故郷を欣懐した。
Reading the old letters, he thought happily of his hometown.
懐かしむ is the common modern verb for fondly remembering or missing something, while 欣懐 is a rare literary equivalent.
The exact derivation is uncertain; the kanji 欣 (rejoice) and 懐 (bosom, cherish) suggest a classical compound meaning 'to hold joyfully in one's heart'.