The best replacement for outlier is influential observation.

The best alternatives to outlier are rated as following:
★★★★★  influential observation
★★★★  influential point
★★★  swrve
★★★  outliers
★★  outlier
★★  leverage point
★★  mastermind

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Speaking about outlier, one probably shouldn't forget about mean.

Other search terms related to outlier and their ratings are:
★★★★★ mean
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