MonthName - with\without Abbrevation
Private Sub CommandButton1_Click()
Dim max As Integer
max = 12
For i = 1 To max
Range("A" & i).Value = MonthName(i, True)
Range("B" & i).Value = MonthName(i, False)
Next
Columns(1).AutoFit
Columns(2).AutoFit
End Sub