Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ambŭlācrum, i, n. [ambulo], a walk planted with trees, commonly near a house (only ante-and post-class. for the class. ambulatio), Fest. p. 18: senex Gynaeceum aedificare volt hic in suis Et balineas et ambulacrum et porticum, Plaut. Most. 3, 2, 69: longa et mollia ambulacra, * Gell. 1, 2, 2; Pall. 1, 18, 2.