An example of an individual synecdoche is the following, used by Mr. Lockwood to describe Hareton's entrance into the Wuthering Heights kitchen in the morning. Mr. Lockwood, having had a rough night of it in the dead Catherine's room, is snoozing on a bench near the fire. Rather than say that a person has entered, Lockwood notes:
A more elastic footstep entered next ...
Obviously a "footstep" doesn't enter by itself, and in this case, the footstep stands for an entire human body.
A more interesting and far-reaching use of synecdoche, in my opinion, is the use of "moors" to describe Catherine's love of nature and freedom. Of course, she does love the moors themselves, but they stand more generally for her love of the outdoors and being liberated from the stifling constraints of civilization and patriarchy. One intuitively knows that were Catherine, say, transported to Egypt, she would long to be running by the Nile or in the desert sands. The "moors" are a stand-in for the nature/civilization contrast on which the novel draws.