1) As an adjective, crowded, busy or engaged.
1620 all throng in work for tearmers [sic] going downe, Brandsby
1677 being very throng that day below some went into that false-floore, Northowram
1705 the house being very throng with guests, West Riding
1774 to York on foot, the City was very throng. Occasionally it may have implied ‘too busy' : 1704 We are very Throng about setting the Engine in the Colliery, Masham.