Manthanein - is that a Greek word meaning learning ? What are its different verb forms ? I found the word missing in current Greek dictionaries. Perhaps its become archaic. sinhakumara. 
It means “to learn.” In Modern Greek it’s μαθαίνω (pres.), έμαθα (aor.), μαθεύτηκα (aor. pass.), μαθημένος (past participle).
In Ancient Greek the forms were μανθάνω (pres.), μαθήσομαι (fut.), ἔμαθον (aor.), μεμάθηκα (perf.), no perfect passive or aorist passive.
many many thanks, Damoetas !! You’ve been a great help. Though I"ve begun to wonder what your name could possibly mean !! sinhakumara. 
Oh! I got that name from a character in Vergil’s Eclogues (and Vergil himself took it from Theocritus’ Idylls). I especially like the fact that Eclogue 3 begins with this unusual line:
Dic mihi, Damoeta, cuium pecus? an Meliboei?
‘Tell me, Damoetas, whose flock is this? Meliboeus’?’
The word for ‘whose’, cuium, is very odd for Latin (the standard form would be cuius). So someone in late antiquity wrote a parody of that line, which goes,
Dic mihi, Damoeta, ‘cuium pecus’ anne Latinum?
‘Tell me, Damoetas, “cuium pecus” - is that Latin?’