Able to be converted, changed, or transformed from one form to another; capable of conversion.
From Latin 'convertibilis,' combining 'convertere' (to turn around, transform) with '-able' (capable of being). An alternate, older spelling of 'convertible' that is now less common.
'Convertable' is simply an older or non-standard spelling variant of 'convertible'—most style guides recommend 'convertible' instead, but 'convertable' still appears in older documents and some technical contexts.
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