I reported an issue with the hints. Voll does in fact mean "full", but "thick" and "canned"? What? There should be better hints on this word, really. I put in "it is crowded", and was glad that I got the green check mark, but that definition is not in the hints. Why? It would help people if they knew at least three or four of the actual meanings of the words!
at least "voll" sounds like "full". And a lot of people are saying they put "thick" instead of "full." English is my first language and I would gladly say "It is full/thick" when referring to hair. However, in this instance, think of it as a cup being full. You wouldn't yell "It is thick!" when the cup is overflowing you would most likely yell "It is full."