For all time in the future; forever and ever without end.
Compound of 'forever' + 'more' (an archaic/poetic intensifier), creating a redundant but emphatic expression used mainly in older poetry and formal speech.
'Forevermore' is basically 'forever' with extra emphasis—it's like saying 'forever more,' as in 'even more forever than just forever!' It's the kind of dramatic language Shakespeare would use, and it sounds incredibly romantic but also kind of ridiculous if you think about it.
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