Answer: The best meaning of "gaunt" as it is used in the sentence provided is A. skeletal.
Explanation: "Gaunt" is an adjetive used to describe someone as very thin and haggard. In the sentence provided, the word "gaunt" has been used to describe a sinister figure; therefore, in this case, the best meaning of "gaunt" is "skeletal". "Skeletal" is also an adjective and it makes reference to someone that does not have a lot of flesh, that is to say someone that resembles a skeleton.