Unreliable, disloyal, or changing one's affections and commitments without good reason; fickle in love or friendship.
Compound of 'fickle' (from Old English 'ficol' meaning deceitful) plus 'hearted' (Old English 'heorte'), literally describing someone with an inconstant heart.
This compound word was especially popular in love poetry and romances to describe people who couldn't keep their romantic promises—Shakespeare would have had a field day with this one!
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