词根词缀：bi-, bin-, bino-, bis-

【来源及含义】Latin: two, twice, double, twofold; a number; it normally functions as a prefix

【相关描述】This bi- is used before s, c, or a vowel. Don't confuse this bi- with another one which means "life".

All words except biennial referring to periods of time and prefixed by bi- are potentially ambiguous. Since bi- can be taken to mean either "twice each" or "every two", a word like "biweekly" can be understood as "twice each week" or "every two weeks".

【同源单词】biacid, biangular, biannual, biannual, biarchy, biarticulate

词根词缀：penna-

【来源及含义】Latin: feather, feathers; by extension in some situations, wing, wings

【相关词根词缀】 Related "feather, feather-like; soft down, plumage" word units: pinni-, pin-; plum-, -plume; pterido-; ptero-; ptilo-.

【同源单词】bipennate muscle, bipennate, brevipennate, empennage, impennate, longipennate