1. to begin to have success with something that you want to do.

They won't even get to first base with the directors with a proposal like that.

2. to get to the first stage of a sexual relationship, where partners kiss and touch each other.

Jimmy hasn't even gotten to first base yet with his girlfriend.

• on the sidelines
• on the side of the angels
• on the sly
• on-the-spot
• on the spot
• on the spur of the moment
• on the starting blocks
• on the strength of
• on the strength of something
• on the stump
• on the table
• on the threshold of
• on the threshold of something
• on the tip of tongue
• on the tip of your tongue
• on the town
• on the trot
• on the verge of
• on the verge of doing something
• on the wagon
• on the warpath
• on the way
• on the whole
• on the wing
• on the wrong side of the law