WordNet (r) 3.0 (2006):
step in v 1: get involved, so as to alter or hinder an action, or through force or threat of force; "Why did the U.S. not intervene earlier in WW II?" [syn: intervene, step in, interfere, interpose] 2: act as a substitute; "She stood in for the soprano who suffered from a cold" [syn: substitute, deputize, deputise, step in]