1590s, "to start with fright (as a startled horse does), shy, take alarm," from Middle English bugge "specter" (among other things, supposed to scare horses at night); see bug (n.); also compare bogey (n.1), boggart.
The meaning " hesitate, stop as if afraid to proceed in fear of unforeseen difficulties" is from 1630s; the transitive sense of "confound, cause to hesitate" is from 1640s. As a noun from 1650s. Related: Boggled; boggling; boggler (from c. 1600 as "one who hesitates").
updated on October 19, 2022