trial run, cardinal (IMPORTANT) , starting point

Israeli soldiers pushed into heavily populated areas of Gaza City Sunday morning. After some heavy fighting with Hamas militants, the Israeli troops pulled back. Everyone says this could have been a trial run for a stronger push into Gaza's urban areas, or it could just be a tactic to apply pressure on Hamas to accept a cease-fire agreement. Prime Minister Ehud Olmert said that while "Israel is getting close to achieving the goals it set" in Gaza, "patience, determination, and effort are still needed."

A cardinal rule of mountain climbing says that when one loses one's way on a mountain, one should return to the starting point. If one continues to wander recklessly, one could end up stranded, as many mountaineering accidents show.

cardinal (IMPORTANT)
adjective [before noun]
of great importance; main:
a cardinal rule/error/sin

starting point noun [C usually singular] (UK ALSO start point)
a place or position where something begins:
The starting point for the guided tour of the town is in the market square.
The committee emphasised that its report was only meant as a starting point for discussion.

trial run noun [C]
a practical test of something new or unknown to discover its effectiveness:
We're holding a tournament in the new ice-hockey stadium, as a trial run for next year's Winter Olympics.