1. (particle) if, if only - often implies the reverse of what is stated and can be used with the verbal particles i, ka, e ... ana and with he.
Me he manu ahau, kua rere atu ki Rarotonga. / If I was a bird I would have flown to Rarotonga.
(Te Pihinga Textbook (Ed. 2): 66-67;)
2. (particle) as if, like - unlike other prepositions, me with this meaning can precede he.
He tino whero, me he pua rātā. / It's bright red, like a rata flower.
(Te Māhuri Study Guide (Ed. 1): 63-64;)
3. (particle) in case ... may, were fortunate, to see whether, if it were not for.
(Te Pihinga Textbook (Ed. 2): 126-127;)