Lookup partial value and return text I define

I want to do a partial lookup on a cell and then return a text value I set. For example: I have a column of dates such as 1/1/13, 4/12/13, 6/1/13. I want to lookup the first number and then return the corresponding month. So 1/1/13 would return a value of January, 4/12/13 would return April, etc.

Thanks!