One who does not live where his office, or business, or estate, is. Bentley. [1913 Webster]
That which lies, or is, away from the main body. [1913 Webster]
A part of a rock or stratum lying without, or beyond, the main body, from which it has been separated by denudation. [1913 Webster]
A datum that lies significantly beyond the main cluster of data points on a graph or diagram; -- suggestive of an error in measurement. [PJC]

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OXFORD DICTIONARY

outlier, n.
1 (also attrib.) an outlying part or member.
2 Geol. a younger rock formation isolated in older rocks.
3 Statistics a result differing greatly from others in the same sample.

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