How to acknowledge my professor who isn't helping much with my master's thesis? the main advisor for my master's thesis is a doctorate student of the professor who oversees my thesis. I had one conversation with the professor at the beginning of my thesis and I'll probably see him the next time at my thesis defense.  

The professor will have final word on the structure and phrasing of the written piece, the topic however is not part of his research. I'm fine with that as the doctorate student is a great help and also knows what the professor wants to see in a thesis. 

Other theses I've read usually praise the professor at the beginning of the acknowledgements.
How can i acknowledge the contribution of my professor in a honest and tasteful manner without making it look like he did nothing compared to the doctorate student?
You could get around it by thanking him for the opportunity to work in his lab and the chance to explore this particular avenue of research.

All at the same time, you can thank the PhD student for all the insightful chats and helping hands throughout the project which should be clear to the reader who was primarily advising you.