tallywag

Origin unknown. Compare tallywhacker, which is attested later.

tallywag (plural tallywags)

1. (uncommon) the black sea bass, Centropristis striata
   • 1890, David Starr Jordan and Carl Eigenmann, A Review of the Genera and Species of Serranidae Found in the Waters of America and Europe, page 391:

     72. CENTROPRISTIS STRIATA. (the black sea-bass, black-fish, tally-wag, hannahill, black-will, black harry)

   • 2014, Bernard Guillas and Ronald Oliver, Two Chefs, One Catch: A Culinary Exploration of Seafood, page 220:

     These are our five favorites: Black Sea Bass ¶ Also called black perch, rock bass, chub, and tallywag

2. (archaic, slang) a penis [18th – 20th century]
   • 1941, D.H. Lawrence, The Merry-Go-Round, Act I, scene 1:

     Mrs. Hemstock (rather faintly): I canna abide to feel a man’s arms shiverin’ agen me. It ma’es me feel like a tallywag post hummin’.

3. (obsolete, usually in the plural) a testicle [17th – 20th century]
   • 1715, Samuel Butler, Posthumous Works in Prose and Verse, page 17‑18:

     And not forget that Pious Prince / Whose Tarriwags it held long since. / What tho’ that Codpiece’s dimension, / Shows something was of large extention

• “tallywag; occ. tarriwag”, in Eric Partridge, The Routledge Dictionary of Historical Slang, 2006.