Proto-Indo-European *swel- "to eat, drink" became Iranian *khvāra- "eating". This combined with Old Persian martiya- "mortal man" to form an unattested compound something like *martikhor, which was borrowed into Greek as μαρτιχόρας martikhoras "man-eater", ie "tiger". This changed to μαντιχώρας mantikhōras and was borrowed into Latin as mantichoras. This was borrowed into English thru French as manticore.
In English, *swel- became swallow.
Old Persian martiya- "mortal man" is from *mer- "to rub away, harm". This root shows up in Persian مردم mardum "man" and مردم گیا mardum-giyā literally "man-plant". This is a possible source of Greek μανδραγόρας mandragoras and Latin mandragora, the mandrake plant.