The word pneumatic typically means adapted for holding or inflated with compressed air. However, there is a double meaning for the word in Brave New World. In the novel, Lenina Crowne is the perfect example of a pneumatic female. Many of the men are attracted to Lenina's pneumatic body type (her bosom and lower back). Pneumatic refers to somebody who has the right curves in the right places. For example, in our society, Marilyn Monroe would considered to be pneumatic.
Aldous Huxley uses the word pneumatic often times to bring up a bigger point about society. He uses the word pneumatic to describe Lenina's body but also a common everyday object; a chair. He uses this comparison in order to prove his point about the way society views the topic of sex. Henry Foster and the other guys that Lenina has slept with views her as an object (to have sex with) instead of a person, similar to a chair. Huxley presents the idea that sex is no longer sacred and people are being degraded every day.