1. to extend partly under something else
2. to lap or fold under

1. the amount by which one thing extends under another
2. a part that extends under something else

Examples

• The roof shingles should underlap by at least two inches.
• Make sure the fabric pieces underlap properly before sewing.
• The metal sheets were designed to underlap for better weatherproofing.
• There was a small underlap where the two panels met.
• The carpenter measured the underlap to ensure proper installation.
• The tiles must underlap to prevent water from seeping through.