It's an early Islamic Umayyad copper fals from the Iberian province (al-Andalus, Spain/Portugal).
This example on Zeno.ru has the same basic design, with an eight-point star in a circle on one side and the same four Kufic syllables (which spell the name of the province) in a circle on the other. If you found or acquired it locally there in Portugal, an Andalusian coin makes sense.
These coins are scarce, and not well catalogued. Even so, they are highly popular with collectors in Spain.
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