locust (n.1) Look up locust at Dictionary.com
"grasshopper, large orthopterous insect noted for mass migrations accompanied by destructive ravages of vegetation," early 14c., borrowed earlier in Old French form languste (c. 1200), from Latin locusta "locust; lobster" (see lobster).
In the Hebrew Bible there are nine different names for the insect or for particular species or varieties; in the English Bible they are rendered sometimes 'locust,' sometimes 'beetle,' 'grasshopper,' 'caterpillar,' 'palmerworm,' etc. The precise application of several names is unknown. [OED]
locust (n.2) Look up locust at Dictionary.com
North American tree, used for ornament and lumber, 1630s, a transferred use (based on resemblance) from locust-tree "carob tree" (1610s), the fruit of which supposedly resembles the insect (see locust (n.1)). Greek akris "locust" often was applied in the Levant to carob pods. In U.S. from late 19c. policemen's clubs were famously made from locust wood (locust-club is attested from 1887).