ure or doubtful meaning and then, but only then, its aid may be sought to remove the obscurity or doubt by reference to the associated words." ? a Russell Motor Car Co. v. United States, 261 U.S. 514, 520, 43 S. Ct 428, 430, 67 L.Ed. 778 (1923). But here, the meaning of the plain words in P § 3771(a)(5) and I (aX8