In the oxford dictionary, the definition of colonize is
Send settlers to (a place) and establish political control over it.
An example sentence with this definition is
I think we should send them to colonize other planets for us.
I have been told that you can substitute the definition of a word for the word. The thing is that it wouldn't make sense for this sentence. It would be 'I think we should send them to send settlers to other planets for us and establish political control over it.' What is the rule for knowing when a word fits in a situation?