existence doubtful

existence doubtful

[ig′zis·təns ′dau̇t·fəl]
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In marine operations, expression used principally on charts to indicate the possible existence of a rock, shoal, and so on, the actual existence of which has not been established.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.