As I understand a discussion some time back on a continental list, (and please any expert linguist stop me
if I'm wrong here), the possibility of ogma/ogam being derived from an ancient word meaning 'furrow' seems to be a fair guess (because no one has really come up with a reasonably acceptable alternative). But, the problem we have here is one of time. This word in its meaning of furrow is no longer present in any of the known Celtic languages. In other words, while today with our knowledge we can look back millennia and guess that Ogma and ogam may have originally derived from this ancient IE word, there is next to no chance that it is understood as anything other than how we see it being used in Irish stories and literature - as the name of a Deity and as a form of written language.