The following definitions are mainly based on works by H. Douglas Brown (1987) and Richards and Rodgers (1986)

Methodology

The word �methodology� is frequently used when �method� would be more accurate. Methodology refers to more than a simple set of methods. It is the rationale and the philosophical assumptions that underlie a particular study. In language teaching, methodology means the study of pedagogical practices in general, including theoretical implications and related research.  It includes what is involved in how to teach.

Approach

The level at which assumptions and beliefs about language and language learning are specified. It also includes ways to apply these assumptions and beliefs to  language teaching.

Method

The level at which theory is put into practice and at which choices are made about the particular skills to be taught, the content to be taught and the order in which the content will be presented. It is the plan for organizing the presentation of language material. It is a plan whose parts do not contradict and which relies on an approach.

(retrieved from http://myenglishpages.com/blog/definitions-of-methodology-and-other-elt-terms/)

Hope this helps.

Cheers,

Valentina