Twaddell \Twad"dell\, n., Twaddell's hydrometer \Twad"dell's hy*drom"e*ter\ [After one Twaddell, its inventor.]

A form of hydrometer for liquids heavier than water, graduated with an arbitrary scale such that the readings when multiplied by .005 and added to unity give the specific gravity.

Source: Webster's Revised Unabridged Dictionary (1913)