I can say in italian it means 'string/twine'. But in latin it has to be linum, i or funiculus, i.
Nice to know in italian spago has also the mean of 'fear' and it could be used as nickname meaning 'coward'.

This, of course, unless your 'spago' is a contraction of the negative of 'pagus': dis-pagus > spagus.

Pagus, i = village, settlement; the typical celtic administrative subdivision of the territory.

In this case, your spago could be the cognomen for a stranger who moved in a diffrent village.