Nor did Witnesses invent the term, they just borrowed it.
and...
http://www.nd.edu/~ndethics/events/fallconfs/jitt.shtml...and from http://www.adrian.warnock.info/2006/06/mlj-monday-speaking-truth-in-love-t4g.htm
The Greek word means ‘professing’, so we may translate the phrase, ‘professing the truth in love’. Many have urged that a very literal translation, though it is not a pleasant one, is ‘truthing’ — ‘but truthing in love’. What the expression conveys is that we are ‘in the truth’ and that we are ‘walking in the truth’. Perhaps the best translation of all would be ‘having or holding the truth in love’.