The Collaborative International Dictionary of English v.0.48:

Aam \Aam\ ([add]m or [aum]m), n. [D. aam, fr. LL. ama; cf. L.
   hama a water bucket, Gr. ?]
   A Dutch and German measure of liquids, varying in different
   cities, being at Amsterdam about 41 wine gallons, at Antwerp
   361/2, at Hamburg 381/4. [Written also Aum and Awm.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Awm \Awm\ ([add]m), n.
   See Aam.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

AWM, or AUME. An ancient measure, used in measuring Rhenish wines it
contained forty gallons.