1. [early 19C+] used as a vaguely indecent oath, e.g. as by jiggers! jigger it! be jiggering well careful! etc.
2. [1910s+] (US, also jigaroo! jigeroo!) a warning that someone hostile, e.g. the police, a teacher, one’s parents, is coming.
[1910s–60s] (US) to be a lookout, to keep a lookout.
[late 19C–1920s] (orig. US) a mild oath, euph. for by Jesus!