noun, na-adjective
Describes the peak or most active stage of an event, season, or situation. Often used in phrases like 〜のたけなわ or 〜もたけなわ.
夏もたけなわですね。
Summer is at its height, isn't it?
パーティーがたけなわのときに、彼は帰ってしまった。
He left when the party was in full swing.
The origin is uncertain. It may be related to classical Japanese たけ (height, peak) and なわ (possibly a suffix), but the exact derivation is unclear.