php array push - associative arrays and keep associative keys

[mikeybuk2002yeahbaby]

I have several associative arrays, each starting with a string key. I also have a master array that i want to use to combine each of these sub arrays. When using array_push though, each array is then given an additional numeric key in the master array.How can i avoid this and push the sub arrays into the master array keeping the keys intact?