Single meaning of 'justification' in Scripture?

Much controversy over the doctrine of justification arises from how the term is employed in Scripture.  Reformers such as John Piper tend to see it as the moment when the righteousness of Christ is imputed into us by our faith in him.  Evangelical dissenters such as N.T. Wright tend to see it as a declaration of membership or kinship in God's covenant relationship with His people.

The debate hinges on how such interpretations fit with various Scriptural passages.  But I wonder:  might the term 'justification' (and its cognates) be used in a non-univocal way throughout Scripture, and even by a single author (viz. St. Paul).

I am neither a biblical nor systematic theologian, and I don't pretend to fully understand and appreciate all the relevant issues.  But from my earnest attempt to understand Scripture as a layman (and by the illumination of the Spirit, from an evangelical point of view) and having read more theological texts concerning this issue than the average layman, I see no reason to think that the term is being applied univocally across the board.  If so, then it is up to the systematic theologian to construct a concept of justification that is faithful to some concept in the Scripture, even if there are syntactically similar terms that are employed in Scripture that differ in sense.  Furthermore, it seems that it would be a futile attempt to see if one's concept is supported by every instance of that term; rather, one should see if the concept is found in Scripture and attempt to embed it in overall framework that takes into account the other theological concepts in Scripture.

The same seems to be true of other concepts, e.g. grace, faith, righteousness, etc.  It is not obvious to me at any rate that terms such as 'grace' are being applied univocally--e.g., "stewardship of grace", "grace and peace to you", "justified by faith through grace", etc.  For instance, a standard meaning given to 'grace' by evangelicals is something along the lines of "unmerited favor"; but it is hard to see how that works ("the stewardship of unmerited favor" seems not to be what Paul is saying in Ephesians).