Dear V T John,
I don't think the name Anthimus is of Semitic (Hebrew/Syriac) origin. It is a Greek name. So in the Syriac, it may have been written/pronounced as Aatheemos; but in Greek it is Ἄνθιμος (Ἄ = Alpha or A, ν = nu or n, θ = teta or th, ι = iota or i, μ = mu or m, o = omricon or o, and ς = sigma or s).
The father that we commemorate in the 5th Thubden is Anthumus the Patriarch of Constantinople.
He held on to same mia-physite Christology of Mor Severus of Antioch and Mor Dioscorus of Alexandria as opposed to the dia-physite Christology of Chalcedon and Leo of Rome.
Mathew G M