The word 'sidle' is a verb and you can use the word usually in association with a verb or a preposition. The meaning that can be figured out of the word is that of to walk somewhere mostly in a shy or uncertain way. Basically someone is involved in this act only when he does not want to be noticed. The following sentence can make you understand the word well as the word is being used in the context: When John returned from the late-night parties he usually sidled away to his room, so that his father couldn't notice him. The above mentioned sentence says that John felt it bad when he attends late-night parties; he slowly slips into his room so that his father can't say a word to him.