(US politics) The effect that a candidate for the corresponding political office (especially the office of President of the United States) can have on a close political election, when their candidacy results in the election being won by a candidate dissimilar to them, rather than a candidate similar to them.

(voting theory) the effect a minor party candidate with little chance of winning has upon a close election, when that candidate's presence in the election draws votes from a candidate similar to them, thereby causing a candidate dissimilar to them to win the election.

(chemistry) the mesomeric effect

(chemistry) the increased stability of organic compounds having alternate single and double bonds

(chemistry, physics) The characteristic change in optical rotatory dispersion and/or circular dichroism in the vicinity of an absorption band of a substance.

Alternative spelling of side effect

To alter as a side effect.

An unintended consequence of any action in addition to the intended consequence of that action.

The apparent change in frequency or wavelength of a wave that is perceived by an observer moving relative to the source of the waves.

(physics) The zero-voltage current of paired electrons through a weak connection between superconductors.