A variant or dialectal term, possibly referring to a builder, someone who works with boulders, or a regional geographic feature.
Possibly from 'build' plus '-er,' or from 'boulder' plus '-er.' The exact etymology is uncertain, and it may be primarily a regional or obsolete term.
Sometimes words sit on the boundary between standard English and dialect, appearing in some dictionaries but not others. 'Bulder' might be one of these in-between words that different communities recognized differently.
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