忻 is an old equivalent of 欣 ('glad'); modern Chinese uses 欣 for that meaning. Today 忻 survives mainly in the place name 忻州 in Shanxi and in personal names. The heart radical 忄 gives the joy sense; 斤 supplies the sound.
register
Archaic and literary, except as a fixed proper noun. For the 'glad' sense always write 欣 in modern text.
