Adverb taking the 'to' particle, Adverb (fukushi)
for a long time; at (great) length; lengthily; long-windedly; tediously
先生は時間を守ることの大切さについて長々と述べた。Our teacher dwelt on the importance of punctuality. (extending) far; (stretching) out; (lying down) at full length
Also written 長長【ながなが】、永々【ながなが】、永永【ながなが】