An "associate" of key-word X is another key-word (Y) which co-occurs with X in a number of texts. It may or may not co-occur in proximity to key-word X. (A collocate would have to occur within a given distance of it, whereas an associate is "associated" by being key in the same text.)
For example, in a key-word database of Guardian newspaper text, wine was found to be a key word in 25 out of 299 stories from the Saturday "tabloid" page, thus a key key word in this section. The top associates of wine were: wines, Tim, Atkin, dry, le, bottle, de, fruit, region, chardonnay, red, producers, beaujolais.
It is strikingly close to the early notion of "collocate".
Association operates in various ways. It can be strong or weak, and it can be one-way or two-way. For example, the association between to and fro is one-way (to is nearly always found near fro but it is rare to find fro near to).