Power

Weber, 1947
The probability that one actor within a social relationship will be in a position to carry out his will despite resistance, regardless of the basis on which this probability rests.

Weber, Max. The theory of economic and social organization. Trans. AM Henderson and Talcott Parsons. New York: Oxford University Press 1947:152

Foucault, 1983
a mode of action which does not act directly and immediately on others. Instead it acts upon their actions: an action upon an action, on existing actions or on those which may arise in the present or the future … it incites, it seduces, it makes easier or more difficult; in the extreme it constrains or forbids absolutely.

Foucault, M. "The Subject and Power." In Michel Foucault: Beyond Structuralism and Hermeneutics (2nd Ed.). Hubert L. Dreyfus and Paul Rabinow, 208-26. Chicago: University of Chicago Press. 1983:220

Renzetti, 1992
The ability to influence others, the ability to get others to do what one wants them to do regardless of whether or not they want to do it

Renzetti, Claire M. Violent betrayal: Partner abuse in lesbian relationships. Sage Publications, Inc, 1992:43