The Collaborative International Dictionary of English v.0.48:
Scad \Scad\, n. [Gael. & Ir. sgadan a herring.] (Zool.)
(a) A small carangoid fish (Trachurus saurus) abundant on
the European coast, and less common on the American. The
name is applied also to several allied species.
(b) The goggler; -- called also big-eyed scad. See
(c) The friar skate. [Scot.]
(d) The cigar fish, or round robin.