Language: Mandarin Chinese
Origin of term: Collector's jargon
Yànmáodāo literally means "goose-quill-saber". It is defined by having a straight or very nearly straight blade that sweeps up gently from around the last quarter of the blade length.
The yànmáodāo is a transitional phase between the zhíbèidāo and sabers curved over their entire length. The first yànmáodāo seemed to have originated in the Ming dynasty and their use extended well into the Qing.
Yànmáodāo are rarely encountered on the market today, most examples appear to date from the 18th century after which the style seemed to have fallen out of fashion.
A 17th century yanmaodao.
Origin of the term
The term yànmáodāo is modern-day collector's jargon that I have not yet been able to find in classical texts. It is probably synonymous to the yànlíngdāo, a term that turns up in a number of old poems.
The first occurrence of yànlíngdāo in literature seems to be in a Song dynasty poem from the 13th-century encyclopedia called Ocean of Jade by Wang Ying-lin. Chapter 151:
“In the first year of Qiandao（1165）, the military workshops made three thousand goose-feather sabers in a single order.”
Perhaps not coincidentally it is in the Song dynasty that we see the rising popularity of curved edges in use in China in favor of the straight zhíbèidāo (直背刀) or "straight back saber" that had been in common use up until then.
Another mention of yànlíngdāo is in a poem by Ming emperor Jiajing who ruled from 1521 to 1567, about sending off his general Mao Bowen:
“The general heads on his southern campaign, vital and courageous.
Worn across his waist his autumn water goose-feather saber.”
Philip Tom's article Of Geese and Willows.
Peter Dekker's article A typology of Chinese sabers.